-6.93% is the change from 231 to 215
Calculation steps:
[( 215 - 231 ) ÷ 231] x 100 = -6.93%
Formula
Percentage change = [(215 - 231) / 231] x 100
Subtract the new number by the original number
215 - 231 = -16
-16 ÷ 231 = -0.06926406926406926
-0.06926406926406926 x 100 = -6.93%