Question 320900
Well, these are very simple and basic problem. 
Let (xo, yo) a point, and a given line with the equation of y = ax + b
If (xo, yo) is on the given line, we must have yo = axo + b.
For these two problem, you just substitute the value of xo - the given x-coordinates, and you will easily find their y-coordinates.
Example for the line y = 1/2x -4 and the point (0,y1) -> we have y1 = (1/2)*0 - 4 = -4, so the finding point is (0,-4).
Very simple, right? Hope you can get through the others easily.