-8.57% is the change from 350 to 320
Calculation steps:
[( 320 - 350 ) ÷ 350] x 100 = -8.57%
Formula
Percentage change = [(320 - 350) / 350] x 100
Subtract the new number by the original number
320 - 350 = -30
-30 ÷ 350 = -0.08571428571428572
-0.08571428571428572 x 100 = -8.57%