Question 666162
Remember for point x_1,y_1 and x_2,y_2 we have that M(x,y) = (x_1+x_2)/2 , (y_1+y_2)/2

For notation let M_x be the midpoint's x coordinate and similarly let M_y be the midpoint's y coordinate.

Then M_x = (x_1+x_2)/2  and M_y = (y_1+y_2)/2.

This should be sufficient to solve.