Determine the moment about the origin O of the force F = −(5 N)i − (2 N)j + (3 N)k which acts at a point A. Assume that the position vector of A is

(a) r = (4 m)i − (2 m)j − (1 m)k,

(b) r = −(8 m)i + (3 m)j + (4 m)k,

(c) r = (7.5 m)i + (3 m)j − (4.5 m)k.