15X8= 120 (points)
120-84=36 (point)
8+4= 12 (point)
36÷ 12=3 channels
Doing it right is 15-3= 12 (Dao)
Equation:
Assuming that x is right, then 15-X is wrong.
8X-4( 15-X)=84
8X-60+4X=84
X= 12