-19.75% is the change from 400 to 321
Calculation steps:
[( 321 - 400 ) ÷ 400] x 100 = -19.75%
Formula
Percentage change = [(321 - 400) / 400] x 100
Subtract the new number by the original number
321 - 400 = -79
-79 ÷ 400 = -0.1975
-0.1975 x 100 = -19.75%