-34.66% is the change from 978 to 639
Calculation steps:
[( 639 - 978 ) ÷ 978] x 100 = -34.66%
Formula
Percentage change = [(639 - 978) / 978] x 100
Subtract the new number by the original number
639 - 978 = -339
-339 ÷ 978 = -0.34662576687116564
-0.34662576687116564 x 100 = -34.66%