-86.42% is the change from 670 to 91
Calculation steps:
[( 91 - 670 ) ÷ 670] x 100 = -86.42%
Formula
Percentage change = [(91 - 670) / 670] x 100
Subtract the new number by the original number
91 - 670 = -579
-579 ÷ 670 = -0.8641791044776119
-0.8641791044776119 x 100 = -86.42%