-90% is the change from 390 to 39
Calculation steps:
[( 39 - 390 ) ÷ 390] x 100 = -90%
Formula
Percentage change = [(39 - 390) / 390] x 100
Subtract the new number by the original number
39 - 390 = -351
-351 ÷ 390 = -0.9
-0.9 x 100 = -90%
Example