-34.6% is the change from 977 to 639
Calculation steps:
[( 639 - 977 ) ÷ 977] x 100 = -34.6%
Formula
Percentage change = [(639 - 977) / 977] x 100
Subtract the new number by the original number
639 - 977 = -338
-338 ÷ 977 = -0.345957011258956
-0.345957011258956 x 100 = -34.6%