What is the scale factor of this dilation?

5/3

Step-by-step explanation:

on both sides we can see that the orginal length of 3 increased to five

therfore if we multiply 3 by 3/5 we get five which means the scale factor is 5/3

the barter

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.