Determine the moment about the origin O of the force F = − (1.5 lb)i + (3 lb)j − (2 lb)k which acts at a point A. Assume that the position vector of A is

(a) r = (2.5 ft)i − (1 ft)j + (2 ft)k,

(b) r = (4.5 ft)i − (9 ft)j + (6 ft)k,

(c) r = (4 ft)i − (1 ft)j + (7 ft)k.