Solve the below problem:
Q: Determine the moment about the origin O of the force (3 lb) (6 lb) (F= i- j+4 lb) k which acts at a point A. Assume that the position vector of A is
(a) r = -(7.5 ft)i + (3 ft)j - (6 ft)k,
(b) r = -(0.75 ft)i + (1.5 ft)j - (1 ft)k,
(c) r = - (8 ft)I +(2 ft)j - (14 ft)k.