In an MPLS (Multiprotocol Label Switching) network, the routers are typically categorized into different roles. A P (Provider) router is responsible for forwarding packets based solely on the MPLS label and does not handle traffic from the external networks. In this case, R3 is located between other routers and is not directly connected to the external networks, which makes it a P router. Additionally, a transit router is any router that forwards traffic through the MPLS network, and R3 performs this role as it forwards traffic between R1, R2, R4, and R5. Hence, the correct options are that R3 is considered a P router and a transit router.