y=56
What I did:
Both triangles are proportional so I made a proportion:
I got 30 (QP) from the small triangle which side is proportional with 48 on the other triangle side (YX).
30 35
---- = ----- 35*48=30y --------> 1680=30y-------> 1680/30=30y/30----> y=56
48 y
That's pretty much what I did.
Hope this helps :)