Which could be the area of one lateral face of the triangular prism? - 7.5 ft² - 15 ft² - 20 ft² -39 ft²

Becca wants to mix fruit juice and soda to make a punch. she can buy fruit juice for $3 a gallon and soda for $4 a gallon. if she wants to make 28 gallons of punch at a cost of $3.25 a gallon, how many gallons of fruit juice and how many gallons of soda should she buy?