A greenhouse has 4 rows of oak trees and 7 rows of pine trees. Each row of oak trees has 10 trees 25 feet or taller and 5 trees shorter than 25 feet. Each row of pine trees has 6 trees 25 feet or taller and 14 trees shorter than 25 feet. A tree from one of these rows is selected at random. What is the probability of selecting an oak tree, given that the tree is 25 feet or taller?