-25% is the change from 28 to 21
Calculation steps:
[( 21 - 28 ) ÷ 28] x 100 = -25%
Formula
Percentage change = [(21 - 28) / 28] x 100
Subtract the new number by the original number
21 - 28 = -7
-7 ÷ 28 = -0.25
-0.25 x 100 = -25%
Example