How to do this question plz

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

The art class is planning to paint a mural on an outside wall. this figure is a scale drawing of the wall. width: 11 in length: 28 in unit rate: 1.5 ft per in. write the ratio of the area of the drawing to the area of the actual mural. write your answer as a unit rate. show that this unit rate is equal to the square of the unit rate 1.5 ft per in

Ithink i know it but i want to be sure so can you me out ?