-80.75% is the change from 639 to 123
Calculation steps:
[( 123 - 639 ) ÷ 639] x 100 = -80.75%
Formula
Percentage change = [(123 - 639) / 639] x 100
Subtract the new number by the original number
123 - 639 = -516
-516 ÷ 639 = -0.8075117370892019
-0.8075117370892019 x 100 = -80.75%