Answer:
increase of 40%
Step-by-step explanation:
A percentage change is found by ...
percent change = ((new value) -(original value))/(original value) × 100%
= (21 -15)/15 × 100% . . . . . . change from 15 to 21
= 6/15 × 100% = 40%
The change is an increase of 40%.
