-20% is the change from 420 to 336
Calculation steps:
[( 336 - 420 ) ÷ 420] x 100 = -20%
Formula
Percentage change = [(336 - 420) / 420] x 100
Subtract the new number by the original number
336 - 420 = -84
-84 ÷ 420 = -0.2
-0.2 x 100 = -20%
Example