Can someone please help me with finding x:)

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

Aswim teacher sells lesson packages. the best deal has the highest ratio of lessons to total cost.swim lesson packagesnumber of lessons total cost$10$4010 1 $8015$80which package is the best deal? l lesson for $105 lessons for $4010 lessons for $8015 lessons for $80mark this and returnsave and exit

Ineed to know the answer to this algebra question.