You are 100% right for question a and you have a good start on b!
Explanation:
For (ii) of part a, you could also say that since the friction force is in the opposite direction of the pushing force, that the friction is '-60N' The negative sign just shows the direction of friction relative to the pushing force. But for the magnitude the signs are not important.
For part b,
work done equals force × distance
w = F×d
In this case, the worker is pushing with 60 newtons, and the distance is 28m.
Therefore,
w = 60N×28m
w = 1680j
(Or 1.7kj)
Great job! You got most of it!
