This problem is about counting the number of ways to arrange 7 trees in a row, where some of the trees are identical. One way to approach this is to use the formula for permutations of n objects, where r of them are identical of one type, s of them are identical of another type, and so on. The formula is n!/(r!s!...), where n is the total number of objects, and r, s, ... are the numbers of identical objects of each type. In this case, n = 7, r = 2, and s = 5, since we have 2 identical apple trees and 5 identical pear trees. So the number of distinct arrangements is 7!/(2!5!) = (7*6*5!)/(2*5!) = (7*6)/2 = 21. 
A nursery employee wishes to plant 2 identical Golden Delicious apple trees and 5 identical Bartlett pear trees in one row. How many distinct arrangements are possible?