-87.38% is the change from 642 to 81
Calculation steps:
[( 81 - 642 ) ÷ 642] x 100 = -87.38%
Formula
Percentage change = [(81 - 642) / 642] x 100
Subtract the new number by the original number
81 - 642 = -561
-561 ÷ 642 = -0.8738317757009346
-0.8738317757009346 x 100 = -87.38%