-34.19% is the change from 971 to 639
Calculation steps:
[( 639 - 971 ) ÷ 971] x 100 = -34.19%
Formula
Percentage change = [(639 - 971) / 971] x 100
Subtract the new number by the original number
639 - 971 = -332
-332 ÷ 971 = -0.3419155509783728
-0.3419155509783728 x 100 = -34.19%