First divide the new amount (7.28) by the original amount (7) and then times by 100
7.28 / 7 x 100 = 104
This tells us that 7.28 is 104% of 7
Minus this by 100 to get the sales tax rate:
104 - 100 = 4%
You could also subtract 7.28 by 7 first, then divide that by 7 and then multiply by 100:
7.28 - 7 = 0.28
0.28 / 7 x 100 = 4%
