(i) As the displacement is zero in 1st case.
So, work done = zero.
(ii) The work done in pulling a cart by the bullock will be +ve. As A and s are in same direction.
(iii) Work done in case of pulling a trolley by the girl will be +ve. As force and displacement are in same direction.
(iv) As there is no displacement, so work done by a person standing with a heavy bag on his head is zero.