P needs to be something that is multiplied through 5-2n to equal 5/6-1/3n. Since you see that there is a 5 of somesort in both equations an easy place to start is simply making p=1/6. Once you do that then 5*1/6=5/6 so the first part is okay. Then 2n*1/6=2n/6 which is able to be reduced to n/3.
Based on this it is clear that p should equal 1/6.
