Determine the moment about the origin O of the force (7.5 N) (3 N) (4.5 F= i+ j − N)k which acts at a point A. Assume that the position vector of A is
(a) r= −(6 m)i+ (3 m)j + (1.5 m)k,
(b) r=(2 m)i−(0.75 m)j−(1 m)k, (c) r= −(2.5 m)i −(1 m)j+(1.5 m)k.