The midpoint is located at the average of the two x-values and the average of the two y-values, whether or not that point has whole number coordinates.
3+7 —— = 5 2
-8 + 3 ——— = -2.5 (or -5/2) 2
So the midpoint is (5, -2.5). Notice this doesn’t have an integer coordinate for the y-value.