-69.4% is the change from 840 to 257
Calculation steps:
[( 257 - 840 ) ÷ 840] x 100 = -69.4%
Formula
Percentage change = [(257 - 840) / 840] x 100
Subtract the new number by the original number
257 - 840 = -583
-583 ÷ 840 = -0.694047619047619
-0.694047619047619 x 100 = -69.4%