15 points answer asap. no guessing multiply. (9×105)⋅(9×107) (a) 8.1×1012(b) 9×1012 (c) 8.1×1013 (d) 9×1013

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?