Given, Jackie has 250 laptops in his shop.
If the first customer to the shop buys 5x number of laptops, then the number of laptops now left with Jackie in his shop is '250−5x'.
If the second customer to the shop buys 50 more laptops than what the first customer has bought, then it means that the second customer has bought 5x+50 laptops
Hence the number of laptops left with Jackie in his shop is '250−5x−(5x+50)'.