A light horizontal rod 2.0m long is attached to a wall by a frictionless pivot at its left end. Two downward forces act on the rod: 30N at a point 0.50m from the pivot and 20N at a point 1.5m from the pivot. To keep the rod in rotational equilibrium, an upward vertical force F must be applied at the right end. What is the magnitude of F?
a) 27.5N
b) 45N
c) 22.5N
d) 15N