Answer: The function of Rae's earnings : 
She would make $81 after 4 hours.
Step-by-step explanation:
Let x be the number of hours Rae works.
Given : Rae earns $60 for playing music on Saturday nights at the local coffee house. She makes an average of $5.25 in tips per hour.
Then , the function of Rae's earnings will be :_

Now, for x = 4 hours , we get

Hence, she would make $81 after 4 hours.