write business invitation letters for US Visa

Required 3 letter . 1. letter from USA company to the invited person and his company for the purpose of invitation to attend business seminar, also mention to send the scannned copy of visa (after its issued) to confirm the flight and hotel bookings 2nd to US embassy in India from USA company explaining the purpose of invitation and requesting the visa approval and assuring all the expenses including both side flight , hotel accommodation and travel expenses during the stay in US will be given by US Company 3rd , The indian company giving NOC to the person for the traveling to US for a date range