-39.47% is the change from 646 to 391
Calculation steps:
[( 391 - 646 ) ÷ 646] x 100 = -39.47%
Formula
Percentage change = [(391 - 646) / 646] x 100
Subtract the new number by the original number
391 - 646 = -255
-255 ÷ 646 = -0.39473684210526316
-0.39473684210526316 x 100 = -39.47%