How do you solve this problem and what does the answer end up being?
A stamp collection consists of 8-cent, 13-cent and 18 cent stamps. The number of 8-cent stamps is twice the number of 18-cent stamps. There are 3 more 13-cent stamps than 18-cent stamps. The total value of stamps in the collection is $3.68. Find the number of 8-cent stamps in this collection.