-4.2% is the change from 667 to 639
Calculation steps:
[( 639 - 667 ) ÷ 667] x 100 = -4.2%
Formula
Percentage change = [(639 - 667) / 667] x 100
Subtract the new number by the original number
639 - 667 = -28
-28 ÷ 667 = -0.041979010494752625
-0.041979010494752625 x 100 = -4.2%