Principle of Work and Energy

Well, I've just did several questions from the exercise books from the university.

The questions are pretty straightforward. However, there are several skills that I need to brush up before feeling so confident about myself.

1- I have to first understand what the question wants then apply the principles I've learnt

2- The direction of the force or vector has to be taken into consideration. If it's opposing the direction in which the force of gravity is acting, then it is negative.

3-All forces resolved vertically, if there's a friction on the plane, it will have to be taken into consideration