Please someone teach me this don't just solve it I wanna learn how to do it thank you!

This is so hard and it’s for a test

The probability that a tutor will see 0, 1, 2, 3, or 4 students is given below determine the probability distribution's missing value.

Me its important ! marge runs an ice cream parlor. her speciality is triple chocolate sundaes.she can prepare 1 sundae every 2 minutes, and she earns $1.20 for each sundae she makes . if she just makes sundaes for a single shift of at most 4 hours and at least 2 hours , which function relates her earnings to the number of minutes she works?