f(x) = ax + b
(0, -4):
f(0) = a•0 + b
f(0) = b ⇒ b = -4
(12, 0):
0 = a•12 + b
0 = 12a - 4
4 = 12a
[tex]a=\frac4{12}=\frac13[/tex]
The equation of the green line:
[tex]\underline{\,y=\frac13x-4\,}[/tex]
or: [tex]y=\frac13x-4[/tex]
[tex]-\frac13x+y+4=0\\\\\underline{x-3y-12=0}[/tex]
