Given a verbal description of a real-world relationship, determine whether that relationship is linear or exponential.

Problem

Ehsan wants to start a chain of emails, which he does by sending an email to 5 of his friends. He asks each of them to send that email to 2 of their friends the next day, and to tell each of their friends to send the email to 2 of their friends the day after, and so on. Let F be the number of people who will receive the email on day t.
How should the relationship between F and t be modeled?
Please choose from one of the following options.
Get 3 answers correct in a row