Example: You have some money in your pocket. You want to buy some snacks for tonight's match but your wife told you to buy one pizza on your way back to home that costs $10. That means that on snacks you can spend (y) :
y ≤ x - 10 where x represents money in your pocket.
This means that from money in your pocket you have to subtract $10 for pizza and out of remaining money you can spend some part of it on snacks or all of it.