-19.16% is the change from 830 to 671
Calculation steps:
[( 671 - 830 ) ÷ 830] x 100 = -19.16%
Formula
Percentage change = [(671 - 830) / 830] x 100
Subtract the new number by the original number
671 - 830 = -159
-159 ÷ 830 = -0.19156626506024096
-0.19156626506024096 x 100 = -19.16%