Respuesta :

From P to M the change on the x axis is 8-2 = 6 units
on the y axis 5-2 = 3 units 
The change on the x axis is negative, on the y axis it is positive. 

Now as M is the midpoint the change from P to M is the same as the change from M to Q. 

Thus M (2-6, 5+3) = (-4, 8)