-19.94% is the change from 321 to 257
Calculation steps:
[( 257 - 321 ) ÷ 321] x 100 = -19.94%
Formula
Percentage change = [(257 - 321) / 321] x 100
Subtract the new number by the original number
257 - 321 = -64
-64 ÷ 321 = -0.19937694704049844
-0.19937694704049844 x 100 = -19.94%