Here is my question

PQ + QS = 14

PQ/PS = PR/PT due to similarity

8/14 = PR / 10.5

10.5 ( 8/14) = PR

PR = 6 units

Since QR is parallel to ST.....then segment QR is parallel to base ST

This sets up the following relationship :

PQ / QS = PR / RT

8 / 6 = PR /RT

4 / 3 = PR /RT

So....we have 7 equal parts to PT

And PR is 4 of them

So PR = (4/7) (10.5) = 6

Thank you both of you(CPhill and ElectricPavlov)