-5.88% is the change from 680 to 640
Calculation steps:
[( 640 - 680 ) ÷ 680] x 100 = -5.88%
Formula
Percentage change = [(640 - 680) / 680] x 100
Subtract the new number by the original number
640 - 680 = -40
-40 ÷ 680 = -0.058823529411764705
-0.058823529411764705 x 100 = -5.88%