If you have a 42 inch deck what size belt should you buy for replacement

Hi,
A bit to little too litle info here. The first riding mowers sold with the Scotts label were green and sold by Kmart. Most were orange and sold by Home Depot. Noma made the Kmart machines. Then Murray bought Noma. The orange machines were made by both John Deere and the Noma division of Murray. I am able to supply pictures of the decks and the part numbers for any of them with more info. Look for the model number tag and post that; rear or under seat of the green, under seat, rear or under left rear fender of the orange ones.
Peace,
Clarke