13.20

First we took $1.32+$1.32=$2.64 and that equaled three bottles of soda. Next we took $2.64+$2.64 and got $5.28 which equaled six bottles of soda.Then we took $5.28+$2.64 and got $7.92 which was nine bottles of soda.After wards we took $7.92 +$2.64 and got $10.56 which was 12 bottles of soda.Last we took $10.56 + $2.64 and got $13.20 which was 15 bottles of soda. By Morgan E. &Chase