Answer:
The midpoint M is (5,7)
Step-by-step explanation:

U(8,9)
V(2,5)
m = [(8+2)/2 , (9+5)/2]
= [(10/2) , (14/2)]
= (5,7)
(Correct me if i am wrong)
Slope of a line passing through two given points
= (y2-y1)/(x2-x1)
For m=3, and substituting coordinates,
3=(1-y)/(4-1)
solve for y
1-y=3*3=9
y=1-9=-8
Answer: y=-8