100% is the change from 39 to 78
Calculation steps:
[( 78 - 39 ) ÷ 39] x 100 = 100%
Formula
Percentage change = [(78 - 39) / 39] x 100
Subtract the new number by the original number
78 - 39 = 39
39 ÷ 39 = 1
1 x 100 = 100%
Example