In this problem we have that
the point P i will assume that is the incenter of triangle ABC.
The point where the angle bisectors intersect is the incenter
so
SP=(1/3)(SC)
substitute the given values
3x-3=(1/3)(7x+5)
solve for x
9x-9=7x+5
9x-7x=5+9
2x=14
x=7
Find the length SC
SC=7x+5
SC=7(7)+5
SC=54 units
Find the length PC
we have that
PC=(2/3)SC
PC=(2/3)(54)
PC=36 units