3450% is the change from 18 to 639
Calculation steps:
[( 639 - 18 ) ÷ 18] x 100 = 3450%
Formula
Percentage change = [(639 - 18) / 18] x 100
Subtract the new number by the original number
639 - 18 = 621
621 ÷ 18 = 34.5
34.5 x 100 = 3450%
Example