Three workers trying to move a 3 × 3 × 4-ft crate apply to the crate the three horizontal forces shown. 

(a) If P = 60 lb, replace the three forces with an equivalent force-couple system at A. 

(b) Replace the force-couple system of part a with a single force, and determine where it should be applied to side AB. 

(c) Determine the magnitude of P so that the three forces can be replaced with a single equivalent force applied at B.