-33.44% is the change from 960 to 639
Calculation steps:
[( 639 - 960 ) ÷ 960] x 100 = -33.44%
Formula
Percentage change = [(639 - 960) / 960] x 100
Subtract the new number by the original number
639 - 960 = -321
-321 ÷ 960 = -0.334375
-0.334375 x 100 = -33.44%