A garden contains 7 rows of tulips and 8 rows of daffodils. Each row of tulips has 6 plants that are at least 18 inches tall and 9 plants shorter than 18 inches. Each row of daffodils has 7 plants that are at least 18 inches tall and 7 plants shorter than 18 inches. If a single plant is selected at random from all the rows, what is the probability that it is a tulip, given it is at least 18 inches tall?