Which other sets are closed under addition

Joey is asked to name a quadrilateral that is also a rhombus and has 2 pairs of parallel sides.should be his answer

Will give a: 122 b: 90 c: 48 d: 180

Sophia wrote an equation to represent the revenue of a movie theater for one day. she let x represent the number of child tickets sold and y represents the nunver of adult tickets sold. if a child ticket cost $4, an adult ticket cost $6, and the total revenue for the daybwas $420, which equation could sophia use to represent the number of chikd and adult tickets that were sold?