Answer:
16
Step-by-step explanation:
Perfect squares are numbers that can be written as the product of a different number and itself: k * k = k^2.
Looking at the numbers:
21: can be written as 3 * 7, but not in the form k^2
15: can be written as 3 * 5, but not in the form k^2
6: can be written as 2 * 3, but not in the form k^2
16: can be written as 4 * 4, which is in the form of k^2
27: can be written as 3 * 9, but not in the form k^2
Thus, the answer is 16.
Hope this helps!
