Bethany sells roses and petunias. The expression 3r + 2.5p gives the cost (in dollars) of r roses and p petunias. What is the cost of 7 roses and 8 petunias?

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?