-30.32% is the change from 917 to 639
Calculation steps:
[( 639 - 917 ) ÷ 917] x 100 = -30.32%
Formula
Percentage change = [(639 - 917) / 917] x 100
Subtract the new number by the original number
639 - 917 = -278
-278 ÷ 917 = -0.3031624863685932
-0.3031624863685932 x 100 = -30.32%