-27.9% is the change from 921 to 664
Calculation steps:
[( 664 - 921 ) ÷ 921] x 100 = -27.9%
Formula
Percentage change = [(664 - 921) / 921] x 100
Subtract the new number by the original number
664 - 921 = -257
-257 ÷ 921 = -0.27904451682953313
-0.27904451682953313 x 100 = -27.9%