-47.5% is the change from 640 to 336
Calculation steps:
[( 336 - 640 ) ÷ 640] x 100 = -47.5%
Formula
Percentage change = [(336 - 640) / 640] x 100
Subtract the new number by the original number
336 - 640 = -304
-304 ÷ 640 = -0.475
-0.475 x 100 = -47.5%