Use the coordinates of the labeled point to find the point-slope equation of
the line.

step-by-step explanation:

points a and b are equidistant from the desired line, so the line you find by using them will go through point r.

using points other than a and b will give the desired line only if they are equidistant from r. if they are randomly located, the perpendicular line you create will not necessarily go through point r, hence will not be a solution to the problem.

using pemdas, (order of operations) you'll see the answer is 24.

sorry not knowing about that