A body constrained to move along the z-axis of a co-ordinate system is subjected to a constant force `vec(F)` given by `vec(F) =- hati +2hatj +3hatk` newton, where `hati, hatj` and `hatk` represen unit vectors along x,y- and z-axis of the system respectively. Calculate the work done by force in displacing the body through a distance of 4m along the z-axis.