Answer:
m = 0, y = -6
Explanation:
using point slope form :

y-y1=m(x-x1) ; initial point (x1,y1) = (4,-6), final point (x,y) = (7,-6).
one substituted, it should look like this:
-6--6 = m(7-4),
-6+6= m(7-4)
0 = m(7-4)
0 = 3m
0/3 = 3/3m
0 = m
m = 0/3 = 0