-7.14% is the change from 420 to 390
Calculation steps:
[( 390 - 420 ) ÷ 420] x 100 = -7.14%
Formula
Percentage change = [(390 - 420) / 420] x 100
Subtract the new number by the original number
390 - 420 = -30
-30 ÷ 420 = -0.07142857142857142
-0.07142857142857142 x 100 = -7.14%