Take every word and translate into math. 

$\displaystyle 4$ more than means that you need to add $\displaystyle 4$ to something. 

$\displaystyle 2$ times something means that you need to multiply $\displaystyle 2$ to Bob's age which is $\displaystyle x$. 

Now we can combine them to have an expression of $\displaystyle 2x+4$.

We have $\displaystyle 3$ known values and $\displaystyle 1$ unknown value. We have a total and that these $\displaystyle 4$ colors add up to $\displaystyle 100$.

Let's represent the colors with variables corresponding to the first letter of the color. $\displaystyle r+g+b+y=100$.

Now, plug in the values that are known. Final answer is $\displaystyle 40+30+15+y=100$. 

To simplify we add the constants which results in:

$\displaystyle 85+y=100 \rightarrow y=15$

Take every word and translate into math. What a difference means, is that $\displaystyle a$ is the first number subtracting $\displaystyle b$.

The $\displaystyle a$ part is $\displaystyle 5$ times something means that you need to multiply $\displaystyle 5$ to something which is $\displaystyle x$.

The $\displaystyle b$ part is quotient. 

Anytime you take a quotient of $\displaystyle a$ and $\displaystyle b$, $\displaystyle a$ is the in the numerator and $\displaystyle b$ is in the denominator. Therefore the expression is $\displaystyle \frac{30}{7x}$. 

Anytime you see "is" means equal.  

$\displaystyle 2$ more than means that you need to add $\displaystyle 2$ to something.

That something is $\displaystyle 4$ multipled by $\displaystyle x$ or $\displaystyle 4x$.

Let's just combine them to have an expression of $\displaystyle 5x-\frac{30}{7x}=4x+2$. 

Let's translate into math equations.

First month is $\displaystyle x.$ Then for the next month, he adds $\displaystyle 30$ to the previous month or $\displaystyle x+30.$ Then, for the next month, he adds another $\displaystyle 30$ to the previous month which was $\displaystyle x+30.$ By adding another $\displaystyle 30$, this month becomes $\displaystyle x+60.$ For the fourth month, it's just another $\displaystyle 30$  added to the previous month which was $\displaystyle x+60.$ The fourth month becomes $\displaystyle x+90$.

With the total given, lets combine the expressions to get $\displaystyle x+x+30+x+60+x+90=900$.

Simplifying this we get:

$\displaystyle 4x+180=900$

Take every word and translate into math. The sum of something means adding. So that would be $\displaystyle x+3$. Is means equals something. Putting it all together, we get $\displaystyle x+3=5$. 

Take every word and translate into math. Difference means subtracting. So we are subtracting $\displaystyle 5$ and $\displaystyle x$. Is means equal something. Putting it all together, we have $\displaystyle 5-x=4$.

Take every word and translate into math. The product of something means multiplying. So we have $\displaystyle 3x$. The sum of something means adding. So that would be $\displaystyle y+7$. Is means equals something. Putting it together, we have $\displaystyle 3x=y+7$. 

Take every word and translate into math. Quotient means dividing, so we have $\displaystyle \frac{x}{5}$. When it's $\displaystyle a$ and $\displaystyle b$, $\displaystyle a$ will always be at the numerator of the fraction. Is means equal something. Difference is subtracting and we are subtracting $\displaystyle a$ with $\displaystyle 7$ times sum of $\displaystyle b$ and $\displaystyle 3$. Times means multiplying and sum means addition. We are multiplying $\displaystyle 7$ with $\displaystyle (b+3)$. There must be parentheses as the sum of $\displaystyle b$ and $\displaystyle 3$ is an expression. Putting it all together, we get $\displaystyle \frac{x}{5}=a-7(b+3)$. 

Take every word and translate into math. Square root means using a radical sign. So we have $\displaystyle \sqrt{x}$. Is means equal something. Next, sum is addition so we have $\displaystyle a+b$. Since it's squared, we have the whole thing in parentheses raised to the second power like so: $\displaystyle (a+b)^2$. It is tempting to think it's $\displaystyle a+b^2$ but if it was, then it should say sum of $\displaystyle a$ and $\displaystyle b$ square. So final answer is $\displaystyle \sqrt{x}=(a+b)^2$. 

Starting with the equation $\displaystyle 2a+9=23$, you want to collect like terms.

Put all of the numbers on one side, and leave only the variable on the other side.

The first step is to subtract $\displaystyle 9$ from both sides.

You get $\displaystyle 2a=14$.

The next step is to divide both sides by $\displaystyle 2$ to get the final answer, $\displaystyle a=7$.