How are amphibians related to reptiles?

Answer 1

Because they are both ectotherms.

Amphibians (class Amphibia; from Greek αμφις"both" and βιος "life") are a taxon of animals that include all living tetrapods (four-legged vertebrates) that do not have amniotic eggs, are ectotherms, and generally spend part of their time on land. Most amphibians do not have the adaptations to an entirely terrestrial existence. There are around 6,000 described, living species of amphibians.

Reptiles (Reptilia; from Latin repere, "to creep") are tetrapods and amniotes, animals whose embryos are surrounded by an amniotic membrane. Today they are represented by four surviving orders: Crocodilia (crocodiles, caimans and alligators), Sphenodontia (tuatara), Squamata (lizards, snakes and amphisbaenids), and Testudines (turtles). Reptiles inhabit every continent except for Antarctica, although their main distribution comprises the tropics and subtropics.

Herpetology (Greek ἑρπετόν herpeton "to creep" and λόγος logos "explanation") is the branch of zoology concerned with the study of reptiles and amphibians.

Answer 2

They are related because millions of years ago reptiles evolved from amphibians, so that makes them pretty close.