What is the missing number in the table

Which expression is equivalent to? assume x > 0 and y > 0.

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

Steve wants to develop a way to find the total cost of any item including sales tax. the sales tax in his city is 6%. his friend jenna writes the expression x + 6x where x is the cost of the item. explain whether her expression is correct based on the situation.