(c) 15 : 16
Let the two squares be ABCD and PQRS.
Further, let the lengths of each side of ABCD and PQRS be x and y, respectively.
Therefore
=
⇒ =
Taking square roots on both sides, we get:
=
Now, the ratio of their perimeters:
= =
⇒ =
⇒ =
Thus, the ratio of their perimeters = 15 : 16