Perimeter of first square = 12
Therefore, Its side = \( \Large \frac{12}{4} \) = 3 cm
and its area = \( \Large 3^{2} \) = 9 sq. cm
Perimeter of second square = 16 cm
Therefore, Its side = \( \Large \frac{16}{4} \) = 4 cm
and its area = \( \Large 4^{2} \) = 16 cm
Therefore, Area of new square = 9 + 16 = 25 sq. cm
Therefore, Its side = \( \Large \sqrt{25} \) = 5 cm