Whaddya mean "solve"? - The coordinates of the midpoint of a line segment are the arithmetic means of the corresponding coordinates of their endpoints. Thus the midpoints are

1.) M1 = ((3+6)/2, (2+7)/2) = (9/2, 9/2)

2.) M2 = ((-4+5)/2, (3-2)/2) = (1/2, 1/2)

3.) M3 = ((6/9+4/9)/2, (2/7+1/7)/2) = (5/9, 3/14)