Nov 8 (Reuters) - U.S.-based telecommunications firm Viasat on Monday agreed to buy rival Inmarsat in a deal valuing the British company at $7.3 billion, as the companies seek to scale up their spectrum, satellite and land-based communication offerings. The deal comprises of $850 million in cash, about 46.4 million shares of Viasat valued at roughly $3.1 billion and the assumption of Inmarsat’s $3.4 billion net debt, Nasdaq-listed Viasat said. (Reporting by Pushkala Aripaka in Bengaluru; Editing by Krishna Chandra Eluri)