-97.73% is the change from 660 to 15
Calculation steps:
[( 15 - 660 ) ÷ 660] x 100 = -97.73%
Formula
Percentage change = [(15 - 660) / 660] x 100
Subtract the new number by the original number
15 - 660 = -645
-645 ÷ 660 = -0.9772727272727273
-0.9772727272727273 x 100 = -97.73%