You can represent the amount of money that Jenna spent by writing an expression based on the information given.
5n (this is the amount she spent on notebooks) + (and) 3r (this is the amount she spent on pens)
5n + 3r would show how much money she spent. If you know how many notebooks she bought and how much each pen costs, you would multiply these numbers by the 5 and the 3 and add them.