90% is the change from 210 to 399
Calculation steps:
[( 399 - 210 ) ÷ 210] x 100 = 90%
Formula
Percentage change = [(399 - 210) / 210] x 100
Subtract the new number by the original number
399 - 210 = 189
189 ÷ 210 = 0.9
0.9 x 100 = 90%
Example