-30.16% is the change from 915 to 639
Calculation steps:
[( 639 - 915 ) ÷ 915] x 100 = -30.16%
Formula
Percentage change = [(639 - 915) / 915] x 100
Subtract the new number by the original number
639 - 915 = -276
-276 ÷ 915 = -0.3016393442622951
-0.3016393442622951 x 100 = -30.16%