Well y=mx +b
M is the slope
B is the y-intercept. You know x, y, and the slope.
You don't know the y-intercept so that is what you need to find
So substitute
Y=mx+b
-1= 3/2(-8)+b
-1=-12+b
Add 12 to both sides
11=b
Now you know the y-intercept
Rewrite the equation
Y=3/2x+11