-4.63% is the change from 670 to 639
Calculation steps:
[( 639 - 670 ) ÷ 670] x 100 = -4.63%
Formula
Percentage change = [(639 - 670) / 670] x 100
Subtract the new number by the original number
639 - 670 = -31
-31 ÷ 670 = -0.04626865671641791
-0.04626865671641791 x 100 = -4.63%