both the points have a coordinate where y is -1, so the equation is simply -1
y=-1
however if you wanted to really show the working out, it looks like this:
y=mx+c
m=change in y/change in x
m=(-1-1)/(-5+0)=0
subsitute one of the coordinates into y=mx+c
-1=0+c
c=-1
so then y=-1
