Advanced Maths. Need step solution

For another group of runners in Besto, a circuit training exercise was designed to build up their stamina. In this exercise, this group of runners from Besto run from a starting point Q to and from a series of points, P1,P2,P3,, increasingly far away in a straight line, In the exercise, they start at O and run stage 1 from O to P, and back to O, then staye 2 from O to P2, and back to O, and so on. The distances between the points are such that OP1=50m,PPP5=100m, P2P3=300m and PnPn+1=3Pn1Pn (see Fig. 1). (ii) Find an expression for the distance run by a runner from Besto who completes n stages of the circuit training exercise. (iii) Hence, find the distance fromed and the direction of travel, of a funiner from Besto undergoing the circuit training exercise after he has rian cyacily 42km