-21.21% is the change from 99 to 78
Calculation steps:
[( 78 - 99 ) ÷ 99] x 100 = -21.21%
Formula
Percentage change = [(78 - 99) / 99] x 100
Subtract the new number by the original number
78 - 99 = -21
-21 ÷ 99 = -0.21212121212121213
-0.21212121212121213 x 100 = -21.21%