Multiply the price of the groceries before tax - $154.92 - by the decimal equivalent of 9% , which is 0.09. Round this tax to the nearest hundredth (cents), then add to the price of the groceries.

Tax: $\displaystyle \$154.92 \cdot 0.09 \approx \$13.94$

Price after tax: $\displaystyle \$154.92 + \$13.94 =\$168.86$

Taking 250% of a number is the same as multiplying that number by 2.5. We therefore take the product:

$\displaystyle 750 \cdot 2.5 = 1,875$

The first thing to do is to determine what two numbers multiply to give you 12.

1 and 12

2 and 6

3 and 4

Now find the difference between each of those pairs. 

$\displaystyle 12-1 = 11$

$\displaystyle 6-2=4$

$\displaystyle 4-3=1$

The difference could be 1, 4, or 11.  Only 4 is an answer choice.

One way to go about solving this problem is to convert the percent into a decimal and multiply your whole number by that in order to get your answer. When converting a percent into a decimal, move the decimal point two spaces to the left:

30% = 0.30

Then, multiply this number times 150:

$\displaystyle 150 \times 0.30 = 45$

Your answer is $\displaystyle 45$.

We can solve for $\displaystyle x$ with the algebraic equation:

$\displaystyle 0.3\cdot x=60$

$\displaystyle x=\frac{60}{0.3}$

$\displaystyle x=200$

We can then calculate $\displaystyle 40\%$ of $\displaystyle x$:

$\displaystyle 0.4\cdot200=80$

We can convert $\displaystyle 40\%$ to $\displaystyle \frac{40}{100}$ or $\displaystyle 0.4$. We can then calculate $\displaystyle 0.4\cdot 80=32$.

The storewide sale discounts the shirt by 50%:

$\displaystyle .5\times \$42=\$21$

Susan also has the 10% off coupon, so she's really paying 90% of the cost of the shirt:

$\displaystyle .9\times \$21=\$18.90$

$\displaystyle 22 \frac{1}{2} \%$ of $\displaystyle 22 \frac{1}{2}$  can be rewritten as 

$\displaystyle \frac{22 \frac{1}{2} }{100} \times 22 \frac{1}{2}$

$\displaystyle = \frac{45}{2} \times \frac{1}{100} \times \frac{45}{2}$

$\displaystyle = \frac{45 \times 1 \times 45}{2 \times 100 \times 2}$

$\displaystyle = \frac{2,025}{400} = \frac{2,025 \div 25}{400\div 25} = \frac{81}{16} = 5 \frac{1}{16}$

 $\displaystyle 8\frac{1}{3} \%$ of $\displaystyle 666 \frac{2}{3} \%$ is equal to:

$\displaystyle \frac{8 \frac{1}{3} }{100} \times 666 \frac{2}{3} \%$

$\displaystyle = \frac{ \frac{25}{3} }{100} \times \frac{2,000}{3}$

$\displaystyle = \frac{25}{3} \times \frac{1 }{100} \times \frac{2,000}{3}$

Cross-cancel:

$\displaystyle \frac{25}{3} \times \frac{1 }{1} \times \frac{20}{3}$

$\displaystyle = \frac{500}{9} = 55\frac{5}{9}$

Taking 8,000%, as a decimal, is equivalent to multiplying it by $\displaystyle 8,000 \div 100 = 80$, so 8,000% of 9,000 is equivalent to 

$\displaystyle 80 \times 9,000 = 720,000$.