We have:
A(-3, -2)
B(7, -2)
C(-1, 4)
The difference between Xc and Xa will be half the difference between the longer and the shorter base.
Xc- Xa = -1 - (-3) = -1 + 3 = 2
The longer base length is given by
Xb - Xa = 7 - (-3) = 7 + 3 = 10
Therefore the shorter base will be 10 - 2×2 = 6 units long.
Hence, we need to find the point that is 6 units on the right of C, which means:
Xd = Xc + 6 = -1 + 6 = 5
Therefore, the correct answer is A) (5 , 4)
Please, note that you could also reason in a simplier way: you need to find a point that is "at the same height as C", which means that it must have the same y-coordinate. The only option, would be A).