-34.27% is the change from 639 to 420
Calculation steps:
[( 420 - 639 ) ÷ 639] x 100 = -34.27%
Formula
Percentage change = [(420 - 639) / 639] x 100
Subtract the new number by the original number
420 - 639 = -219
-219 ÷ 639 = -0.3427230046948357
-0.3427230046948357 x 100 = -34.27%