-3.29% is the change from 639 to 618
Calculation steps:
[( 618 - 639 ) ÷ 639] x 100 = -3.29%
Formula
Percentage change = [(618 - 639) / 639] x 100
Subtract the new number by the original number
618 - 639 = -21
-21 ÷ 639 = -0.03286384976525822
-0.03286384976525822 x 100 = -3.29%