-5.31% is the change from 339 to 321
Calculation steps:
[( 321 - 339 ) ÷ 339] x 100 = -5.31%
Formula
Percentage change = [(321 - 339) / 339] x 100
Subtract the new number by the original number
321 - 339 = -18
-18 ÷ 339 = -0.05309734513274336
-0.05309734513274336 x 100 = -5.31%