Can someone , my son is a little confused and so am i

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

What are the equivalent ratios for 24/2= /3= /5.5=108/ = /15

The amount spent on food and drink by 20 customers is shown below what is the modal amount spent and the median? 40 25 8 36 18 15 24 27 43 9 12 19 22 34 31 20 26 19 17 28