A student raises her grade average from a 75 to a 90. What was the percent of increase in the student’s grade average? Round your answer to the nearest tenth of a percent, if necessary

Here are some formulas...
percent increase = (new number - original number) / original number...* 100
percent decrease = (original number - new number) / original number...* 100

a student raises her grade from a 75 to a 90since it is going from a smaller number to a larger number, u have an increase
percent increase = (90 - 75) / 70* 100
= 15/70 * 100
= 0.2142 * 100
= 21.42 rounds to 21.4% increase

36.50 on sale for 32.12...since it goes from a larger number to a smaller number, u have a decrease
percent decrease = (original number - new number) / original * 100
= (36.50 - 32.12) / 32.12...* 100
= 4.38 / 32.12...* 100
= 0.1363...* 100
= 13.63 rounds to 13.6% decrease

23.5 to 21.2this is a decrease
percent decrease = (original number - new number) / original...* 100
= (23.5 - 21.2) / 23.5* 100
= 2.3 / 23.5* 100
= 0.0979 * 100
= 9.79 rounds to 9.8% decrease