106.8% is the change from 309 to 639
Calculation steps:
[( 639 - 309 ) ÷ 309] x 100 = 106.8%
Formula
Percentage change = [(639 - 309) / 309] x 100
Subtract the new number by the original number
639 - 309 = 330
330 ÷ 309 = 1.0679611650485437
1.0679611650485437 x 100 = 106.8%