-17.38% is the change from 800 to 661
Calculation steps:
[( 661 - 800 ) ÷ 800] x 100 = -17.38%
Formula
Percentage change = [(661 - 800) / 800] x 100
Subtract the new number by the original number
661 - 800 = -139
-139 ÷ 800 = -0.17375
-0.17375 x 100 = -17.38%