First convert the percent into a fraction.
There is a total of 100 percent, so in order to make 20% a fraction, you have to put 20% as the numerator, all over 100% as the denominator, giving you:
20/100 Which simplifies to 1/5
So now the question asks "What is 1/5 of 18,000"?
18,000 is the same as 18,000/1, because anything divided by 1 gives you the same number in return. Now all you have to do is multiply 1/5 with 18,000/1. Numerator with numerator, and denominator with denominator.
(1 * 18,000)/(1 * 5) = 18,000/5 = 3,600.