-20.1% is the change from 831 to 664
Calculation steps:
[( 664 - 831 ) ÷ 831] x 100 = -20.1%
Formula
Percentage change = [(664 - 831) / 831] x 100
Subtract the new number by the original number
664 - 831 = -167
-167 ÷ 831 = -0.2009626955475331
-0.2009626955475331 x 100 = -20.1%