The sale price was 30% off the original price, which means it was on sale for 70% of the original cost ( 100% - 30% = 70%)
To find the original cost, divide the sale price by the percent of the original cost:
21 / 0.70 = 30
The original price was $30
check:
30 x 0.3 = 9 ( amount of discount)
30 - 9 = 21 ( sale price)
