-7.66% is the change from 666 to 615
Calculation steps:
[( 615 - 666 ) ÷ 666] x 100 = -7.66%
Formula
Percentage change = [(615 - 666) / 666] x 100
Subtract the new number by the original number
615 - 666 = -51
-51 ÷ 666 = -0.07657657657657657
-0.07657657657657657 x 100 = -7.66%