-6.84% is the change from 687 to 640
Calculation steps:
[( 640 - 687 ) ÷ 687] x 100 = -6.84%
Formula
Percentage change = [(640 - 687) / 687] x 100
Subtract the new number by the original number
640 - 687 = -47
-47 ÷ 687 = -0.06841339155749636
-0.06841339155749636 x 100 = -6.84%