68.61% is the change from 309 to 521
Calculation steps:
[( 521 - 309 ) ÷ 309] x 100 = 68.61%
Formula
Percentage change = [(521 - 309) / 309] x 100
Subtract the new number by the original number
521 - 309 = 212
212 ÷ 309 = 0.686084142394822
0.686084142394822 x 100 = 68.61%