Find the principal if interest = 3900 Time = 3 Rate = 16% in 3 month

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?

Iknow the answer but the calculator doesn't seem to give the right one

If wxyz is a square, which statements must be true?