Find the arc length of the semicircle. Either enter an exact answer in terms of pi or use 3.14, for π and enter your answer as a decimal.

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?