Apply the slope formula:
[tex]m=\frac{y2-y1}{x2-x1}[/tex]Given the points:
(x1,y1) = (-4, u)
(x2,y2) = (-7,-6)
m = slope = 5
Replacing:
[tex]5=\frac{6-u}{-7-(-4)}[/tex]Solve for u
[tex]5=\frac{6-u}{-7+4}[/tex][tex]5=\frac{6-u}{-3}[/tex][tex]5\cdot-3=6-u[/tex][tex]-15=6-u[/tex][tex]u=6+15[/tex][tex]u=21[/tex]