What is the relationship between 3i Infrastructure and Investment in the context of the input sentence. Choose an answer from: product/material produced; manufacturer; distributed by; industry; position held; original broadcaster; owned by; founded by; distribution format; headquarters location; stock exchange; currency; parent organization; chief executive officer; director/manager; owner of; operator; member of; employer; chairperson; platform; subsidiary; legal form; publisher; developer; brand; business division; location of formation; creator.

COPENHAGEN, July 7 (Reuters) - Investment firms 3i Infrastructure and AMP Capital have agreed to buy Danish shipping company Esvagt for 4.1 billion Danish crowns ($607 million), aiming to tap growing demand for servicing offshore wind farms.

Answer: industry