Question: how are bilbo and frodo related?
Answer: Frodo is the son of Drogo, who is the son of Fosco (son of Largo, Mungo's younger brother). Therefore Bilbo and Frodo share a common ancestor in Balbo, father of Largo and Mungo. Since that makes Bilbo and Drogo second cousins, Frodo is Bilbo's second cousin once removed.