Just for fun

Derek owns a fruit and veg stall and is taking inventory of his stock. He has 12 pineapples left over from yesterday and took 2 deliveries of 4 pineapples this morning. He writes this down and gives the calculation to Jimmy so he can tell a restaurant how many pineapples they're going to deliver. Jimmy rings the restaurant and tell them they're going to deliver 56 pineapples. How many pineapples does Derek have and why did Jimmy say 56?