The answer is (3, 0) for The second endpoint.
Let's start by calling the known endpoint L and the unknown K. We'll call the midpoint M. In order to find this, we must first note that to find a midpoint we need to take the average of the endpoints. To do this we add them together and then divide by 2. So, using that, we can write a formula and solve for each part of the k coordinates. We'll start with just x values.
(Kx + Lx)/2 = Mx
(Kx + 7)/2 = 5
Kx + 7 = 10
Kx = 3
And now we do the same thing for y values
(Ky + Ly)/2 = My
(Ky + -6)/2 = -3
Ky + -6 = -6
Ky = 0
This gives us the final point of (3, 0)
