Find the value of each variable

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oh and if you mind tell me how you found the value because i do not understand how to find the value it would a lot so i can do it on my own.

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?