40% is the change from 30 to 42
Calculation steps:
[( 42 - 30 ) ÷ 30] x 100 = 40%
Formula
Percentage change = [(42 - 30) / 30] x 100
Subtract the new number by the original number
42 - 30 = 12
12 ÷ 30 = 0.4
0.4 x 100 = 40%
Example