-17.9% is the change from 391 to 321
Calculation steps:
[( 321 - 391 ) ÷ 391] x 100 = -17.9%
Formula
Percentage change = [(321 - 391) / 391] x 100
Subtract the new number by the original number
321 - 391 = -70
-70 ÷ 391 = -0.17902813299232737
-0.17902813299232737 x 100 = -17.9%