The missing variables of the midsegment are:
x = 4
y = 6
How to find the length of the midsegment?
For a midsegment, it means it is the middle point of a line which buisects the line into two equal parts.
Thus:
AM = BM
Thus:
3x - 1 = x + 7
2x = 8
x = 4
Similarly:
5y - 10 = 38 - 3y
8y = 48
y = 6