On the second problem, you can select two of the points and make (x,y) coordinates out of them. Then its just like a problem that would say something like "Find the equation of the line that passes through (1,2) and (3,4)" which is a standard algebra problem.

This question is trying to show you a real life situation where someone would want to find the equation through two points (because they want to make a formula relating two things, that they could then use to predict one quantity based on the other)