-40.3% is the change from 670 to 400
Calculation steps:
[( 400 - 670 ) ÷ 670] x 100 = -40.3%
Formula
Percentage change = [(400 - 670) / 670] x 100
Subtract the new number by the original number
400 - 670 = -270
-270 ÷ 670 = -0.40298507462686567
-0.40298507462686567 x 100 = -40.3%