Why do you multiply a percent by a number to find the percent of that number?

Because a percent is a fraction of 1/100 of a whole thing. for example a whole is 200 and we want to find the 37% of it, we would divide 200 over 100 (which is the percent of the whole thing) and the multiply it by 37 (that is the percentage of the part of the whole thing) and we get 74.
74=37% of 200

It would cost about $345.60