30.31% is the change from 640 to 834
Calculation steps:
[( 834 - 640 ) ÷ 640] x 100 = 30.31%
Formula
Percentage change = [(834 - 640) / 640] x 100
Subtract the new number by the original number
834 - 640 = 194
194 ÷ 640 = 0.303125
0.303125 x 100 = 30.31%