**slopes of perpendicular lines are negative reciprocals**. You absolutely need to remember that for the test. That is to say, if you have a line with a slope of 3/5, a line perpendicular to it will have a slope of -5/3.

For this particular problem, we're going to have to use the diagram to figure out the slope of line

*l*, and then use the principle above to figure out the slope of

*n*.

If you look closely at

*l*, you have both its

*x*- and

*y*-intercepts. That gives you an easy way to calculate the slope, which we sometimes simply say is equal to "rise/run". Line

*l*has a rise of -1 while it has a run of 3.

**Slope of line**.

*l*= -1/3That means the slope of line

*m*HAS TO BE the negative reciprocal of -1/3, or

**3**. That's choice (E).

Note that guesstimate works very well here to check your work. Line

*m*is steep and definitely has a positive slope. Don't get caught picking a choice that doesn't indicate as much.