According to the circular power theorem

AD*BD=CD*DT available.

DT=3*6/2=9 circle radius R=5.5 DO=DT-R=3.5.

Make perpendicular to AB and f on AB (I won't spend the picture)

F is the midpoint of AB, so it is easy to find FD= 1.5.

There are similar triangles DOF and DPT.

Then DO/DF=DP/DT

Available DP=2 1

PB=2 1-6= 15