Answer
16
Step by step
The triangles,PRS and PQT are similar.
PS:ST=15:3
=5:1
let PQ=x
PR:RQ
x+4:4
using the PS:ST ratio,
5:1=x+4:4
4×5=1(x+4)
20=x+4
collecting like terms
20-4=x
x=16.
