Please help with this Maths question.
In a triangle diagram, OA = a, and OB = b.
The point P divides OA in the ratio OP:PA = 4:1
The point Q divided AB in the ratio AQ:QB = 2:3
The point R placed at the end of the extended line OB is such that OB:BR = 5:3
(a) Show that PQ=2/5b - 1/5a
(b) Show that P, Q and R lie on a straight line.