-49.77% is the change from 639 to 321
Calculation steps:
[( 321 - 639 ) ÷ 639] x 100 = -49.77%
Formula
Percentage change = [(321 - 639) / 639] x 100
Subtract the new number by the original number
321 - 639 = -318
-318 ÷ 639 = -0.49765258215962443
-0.49765258215962443 x 100 = -49.77%