-52.19% is the change from 640 to 306
Calculation steps:
[( 306 - 640 ) ÷ 640] x 100 = -52.19%
Formula
Percentage change = [(306 - 640) / 640] x 100
Subtract the new number by the original number
306 - 640 = -334
-334 ÷ 640 = -0.521875
-0.521875 x 100 = -52.19%