100% is the change from 45 to 90
Calculation steps:
[( 90 - 45 ) ÷ 45] x 100 = 100%
Formula
Percentage change = [(90 - 45) / 45] x 100
Subtract the new number by the original number
90 - 45 = 45
45 ÷ 45 = 1
1 x 100 = 100%
Example