As you know a line equation in has the following form:

where is a point that line passes through, and is a vector that is parallel to the line.

Returning to your problem, we have a point that the desired line passes through (we may pick or ), but we need the vector .

We may let as vector, try to see that the line will be parallel to .

Thus, the line is

To find the value that line intersects -plane, we have to set the third component (height) of the line to and solve .

I hope you can find it now?