Question 751075
The y axis has the value 0 for all x, i.e x=0 'is' the y axis. (0,y) describes every point as well. 

The distance between two points is similar to the Pythagorean theorem as we take the difference in x and y and solve for the 'third side'. 

(x2-x1)^2+(y2-y1)^2=D^2

(4-0)^2+(-3-y)^2=36

16+(-3-y)^2=36

(-3-y)^2=20

9+6y+y^2=20 

y^2+6y-11=0

You can solve a number of ways to get the two results. 

y=-3+/-2sqr5  or 1.472, -7.472 These are the two points on the y axis.