1. a) Wrong. What is the acceleration of the plane? It's given in the question.
b) This cannot be negative.
Use: $\displaystyle v^2 = v_o\ ^2 + 2as$
2. Read your axes well. The vertical axis gives the speed at any time.
I. The train is NOT at rest. Otherwise, I would be on the horizontal axis.
II. Can you do this one now?
Negative: Right.
Zero: Right.
3. You didn't answer the question completely and your methodology is wrong.
The side you put as adj is in fact the opp side...
Though you used the correct trigonometry ratio...
You need to find the distance East and the distance North the person has to travel to get to the same point.
4. No, that is not it.
Choose two points on the line.
You chose (6, 0) which is good. But (0, 5) is not.