These points aren't even on the line! How can they be intercepts??

You got the slope right, though.

The x-intercept is where y = 0. Solve this for x.

The y-intercept is where x = 0. Solve this for y.

Yes to the first, no to the second. Two perpendicular lines have slopes that have the following property:

So you know that .

Solve for .

Yes. The slope of a line is rise/run. Consider two points on this line, say (-5, 1) and (-5, 6).

which is undefined.

-Dan