31.56% is the change from 640 to 842
Calculation steps:
[( 842 - 640 ) ÷ 640] x 100 = 31.56%
Formula
Percentage change = [(842 - 640) / 640] x 100
Subtract the new number by the original number
842 - 640 = 202
202 ÷ 640 = 0.315625
0.315625 x 100 = 31.56%