Well, first, triangleMOQ is the same as triangleNOR. We can use this similarity to say QO = RO. Aksi we know PR=15, and since N bisects PR, NR=7.5. We can write an equation which states OR^2=(7.5)^2+ON^2. Also, QO+ON=10 so RO+ON=10. Now that we know this, RO has to be more than 7.5 but less than 8.25. Try solving using that and you will have to do a bit more work.