The question that I am having trouble with is:

a) Find the point on the y-axis that is equidistant from the points (2,-1,1) and (0,1,3).

b) Find a point not on the y-axis that is equidistant from the points (2,-1,1) and (0,1,3).

I'm unsure of where to even start, so if anyone can give me any hints or suggestions that would be much appreciated! Please and thank you!