Sandy's orchard has only apple trees and pear trees and she is wanting to add some avocado trees. Currently, there are 4 apple trees for every 3 pear trees. She is wanting to plant enough avocado trees so that she has 2 avocado trees for every 5 pear trees in the orchard. Sandy is planting 18 avocado trees, making the ratio of avocado trees to apple trees be to .