What is p-9/3=2 what is p?

In the 30-60-90 triangle below side s has a length of and side r has a length

If the ratio of sum of the first m and n terms of an ap is m2 : n2 , show that the ratio of its mth and nth terms is (2m − 1) : (2n − 1).

Collin did the work to see if 10 is a solution to the equation r/4=2.4