The 72.0 kg climber in the figure is supported in the "chimney" by the friction forces exerted on his shoes and back. The static coefficients of friction between his shoes and the wall, and between his back and the wall, are 0.75 and 0.60, respectively. What is the minimum normal force he must exert? Assume the walls are vertical and that the static friction forces are both at their maximum. Ignore his grip on the rope.
I know Ffr=mu*F(normal force) we also know that F of the shoes against the wall=-F of wall against shoes. Newtons 3rd Law. I just don't know where to start.