Answer :
[tex]y=mx+b[/tex]
m - slope
[tex]m=-3 \\ y=-3x+b \\ \\ (3,8) \\ y=8 \ for \ x=3 \\ \\ 8=-3 \cdot 3 + b \\ 8=-9+b \\ b=17 \\ \\ \underline{\underline{y=-3x+17}}[/tex]
m - slope
[tex]m=-3 \\ y=-3x+b \\ \\ (3,8) \\ y=8 \ for \ x=3 \\ \\ 8=-3 \cdot 3 + b \\ 8=-9+b \\ b=17 \\ \\ \underline{\underline{y=-3x+17}}[/tex]