To solve this problem we need to use the distributive property. This property is used to multiply a term outside of a set of parentheses by each of the terms in the parentheses. 

$\displaystyle 2\times9=18$

$\displaystyle 2\times x=2x$

Now we have $\displaystyle 18+2x$

This expression is simplified because we cannot add $\displaystyle 18$ to $\displaystyle 2$ because $\displaystyle 2$ has a variable $\displaystyle (x)$ attached to it. 

$\displaystyle 2x$ is equal to $\displaystyle x+x$ because both expressions will name the same number, no matter which number $\displaystyle x$ stands for. 

Let's do a couple of samples!

Solve for $\displaystyle x=2$

$\displaystyle 2(2)=4$ and $\displaystyle 2+2=4$

Solve for $\displaystyle x=5$

$\displaystyle 2(5)=10$ and $\displaystyle 5+5=10$

As you can see, both expressions equaled the same value. 

$\displaystyle 2x=x+x$

$\displaystyle 3x$ is equal to $\displaystyle x+x+x$ because both expressions will name the same number, no matter which number $\displaystyle x$ stands for. 

Let's do a couple of samples!

Solve for $\displaystyle x=2$

$\displaystyle 3(2)=6$ and $\displaystyle 2+2+2=6$

Solve for $\displaystyle x=4$

$\displaystyle 3(4)=12$ and $\displaystyle 4+4+4=12$

As you can see, both expressions equaled the same value. 

$\displaystyle 3x=x+x+x$

$\displaystyle 4x$ is equal to $\displaystyle x+x+x+x$ because both expressions will name the same number, no matter which number $\displaystyle x$ stands for. 

Let's do a couple of samples!

Solve for $\displaystyle x=2$

$\displaystyle 4(2)=8$ and $\displaystyle 2+2+2+2=8$

Solve for $\displaystyle x=5$

$\displaystyle 4(5)=20$ and $\displaystyle 5+5+5+5=20$

As you can see, both expressions equaled the same value. 

$\displaystyle 4x=x+x+x+x$

$\displaystyle 10x$ is equal to $\displaystyle x+x+x+x+x+x+x+x+x+x$ because both expressions will name the same number, no matter which number $\displaystyle x$ stands for. 

Let's do a couple of samples!

Solve for $\displaystyle x=2$

$\displaystyle 10(2)=20$ and $\displaystyle 2+2+2+2+2+2+2+2++2+2=20$

Solve for $\displaystyle x=3$

$\displaystyle 10(3)=30$ and $\displaystyle 3+3+3+3+3+3+3+3+3+3+=30$

As you can see, both expressions equaled the same value. 

$\displaystyle 10x=x+x+x+x+x+x+x+x++x+x$

$\displaystyle 12x$ is equal to $\displaystyle x+x+x+x+x+x+x+x+x+x+x+x$ because both expressions will name the same number, no matter which number $\displaystyle x$ stands for. 

Let's do a couple of samples!

Solve for $\displaystyle x=4$

$\displaystyle 12(4)=48$ and $\displaystyle 4+4+4+4+4+4+4+4+4+4+4+4=48$

Solve for $\displaystyle x=6$

$\displaystyle 12(6)=72$ and $\displaystyle 6+6+6+6+6+6+6+6+6+6+6+6=72$

As you can see, both expressions equaled the same value. 

$\displaystyle 12x=x+x+x+x+x+x+x+x+x+x+x+x$

$\displaystyle 5x$ is equal to $\displaystyle x+x+x+x+x$ because both expressions will name the same number, no matter which number $\displaystyle x$ stands for. 

Let's do a couple of samples!

Solve for $\displaystyle x=3$

$\displaystyle 5(3)=15$ and $\displaystyle 3+3+3+3+3=15$

Solve for $\displaystyle x=5$

$\displaystyle 5(5)=25$ and $\displaystyle 5+5+5+5+5=25$

As you can see, both expressions equaled the same value. 

$\displaystyle 5x=x+x+x+x+x$

$\displaystyle 11x$ is equal to $\displaystyle x+x+x+x+x+x+x+x+x+x+x$ because both expressions will name the same number, no matter which number $\displaystyle x$ stands for. 

Let's do a couple of samples!

Solve for $\displaystyle x=2$

$\displaystyle 11(2)=22$ and $\displaystyle 2+2+2+2+2+2+2+2+2+2+2=22$

Solve for $\displaystyle x=3$

$\displaystyle 1(3)=33$ and $\displaystyle 3+3+3+3+3+3+3+3+3+3+3=33$

As you can see, both expressions equaled the same value. 

$\displaystyle 11x=x+x+x+x+x+x+x+x+x+x+x$

$\displaystyle 6x$ is equal to $\displaystyle x+x+x+x+x+x$ because both expressions will name the same number, no matter which number $\displaystyle x$ stands for. 

Let's do a couple of samples!

Solve for $\displaystyle x=2$

$\displaystyle 6(2)=12$ and $\displaystyle 2+2+2+2+2+2=12$

Solve for $\displaystyle x=4$

$\displaystyle 6(4)=24$ and $\displaystyle 4+4+4+4+4+4=24$

As you can see, both expressions equaled the same value. 

$\displaystyle 6x=x+x+x+x+x+x$

$\displaystyle 7x$ is equal to $\displaystyle x+x+x+x+x+x+x$ because both expressions will name the same number, no matter which number $\displaystyle x$ stands for. 

Let's do a couple of samples!

Solve for $\displaystyle x=3$

$\displaystyle 7(3)=21$ and $\displaystyle 3+3+3+3+3+3+3=21$

Solve for $\displaystyle x=4$

$\displaystyle 7(4)=28$ and $\displaystyle 4+4+4+4+4+4+4=28$

As you can see, both expressions equaled the same value. 

$\displaystyle 7x=x+x+x+x+x+x+x$