coordinate geometry problem

In coordinate geometry:
Given the midpoints of the sides of a triangle: P(2,5), Q(4,2) and R(1,1)
Find the coordinates of the vertices.

And tell me how you solved it.

Fuck me.

b = \vec{RP} + \vec{RQ}, c = \vec{PR} + \vec{PQ} and a = \vec{QP} + \vec{QR}.