Can someone help me with this please

Determine whether the set of whole numbers is closed under addition. explain why the set is or is not closed. give an example.

During your cycling trip, you and your friends often stayed in hostels. the prices of these are listed below. hostel standard room (price per night) with breakfast (price per night) super sleep hostels £22.45 £28.65 normandy nights £18.55 £25 zzzola hostels £24.50 £30.99 belgian beds £11.20 £18.55 night-time rest days ? £33 what is the range in cost for a single night, including both standard room prices and with breakfast prices?

Find the value of x. give reasons to justify your solutions! h ∈ ig