Question

A sweater for $36.00 at 7% sales tax

Answer 1

36.00 * .07 = 2.52 in sales tax
Price of sweater 36.00
Sales tax 2.52
Total cost 38.52

Answer 2

Convert 7% to a decimal: 0.07
Sales Tax = $36.00 x 0.07 = $2.52
Total = $36.00 x 1.07 = $38.52

I use 1.07 for the total because you need ($36.00 x 1) for the actual price of the product, plus ($36.00 x 0.07) for the tax part, so:
($36.00 x 1) + ($36.00 x 0.07) = $36.00(1 + 0.07) = $36.00 x 1.07 = $38.52