You may want to review parallel and perpendicular lines first.
If you need to find the slope of the line parallel or perpendicular to another line, just find the slope of the given line. The slope of a parallel line will be the same. So, if you want to find the slope of a line parallel to y = 2x − 3, the answer is just the same slope, 2.
Perpendicular lines are a bit trickier. Remember, if you multiply the slope of two perpendicular lines, you get −1. So we want the negative reciprocal of the slope of the given line. (That is, we take the reciprocal, and then the negative of that.) So, in our example, we would get −1 ⁄ 2.