so use y=mx+b
m=slope or rise/run
b=y intercept where line passes throught y axis or when x=0
to find slope, do (y1-y1)/(x1-x2)
(x,y)
(3-9)/(-1-(-5))=(-6)/(-1+5)=(-6)/(4)=-3/2
y=-3/2x+b
solve for b by subsituting
3=x
-1=y
-1=-3/2 times 3+b
-1=-9/2+b
Add -9/2 to both sides
-1=-2/2
-2/2+9/2=7/2
7/2=b
the equaiton is
y=-3/2x+7/2
