-20.9% is the change from 646 to 511
Calculation steps:
[( 511 - 646 ) ÷ 646] x 100 = -20.9%
Formula
Percentage change = [(511 - 646) / 646] x 100
Subtract the new number by the original number
511 - 646 = -135
-135 ÷ 646 = -0.2089783281733746
-0.2089783281733746 x 100 = -20.9%