-3.15% is the change from 666 to 645
Calculation steps:
[( 645 - 666 ) ÷ 666] x 100 = -3.15%
Formula
Percentage change = [(645 - 666) / 666] x 100
Subtract the new number by the original number
645 - 666 = -21
-21 ÷ 666 = -0.03153153153153153
-0.03153153153153153 x 100 = -3.15%