We need the metric relations (see image for definition of A & B)
which says
AO^2=OB*OP
or
AB^2=OB*BP
We will use the second one, and substitute values
AB=3
OB=4
AB^2=OB*BP => 3^2=4*BP => BP=3^2/4=2.25
=>
P(4+2.25,0)=(6.25,0)
Using the first relation:
AO=sqrt(4^2+3^2) = 5
OB=4
AO^2=OB*OP => 5^2=4*OP => OP=5^2/4=6.25
=>
x-coordinate of P=6.25