The frequency of a vibrating string varies inversely as it's length. A string 3 feet long vibrates 175 cycles per second. Find the frequency of a 5 foot string.

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?