a1 = 68/4 = 17 cm
and a2 = 60/4 = 15 cm
[ where a1 and a2 are sides]
According to the question,
Area of the third square = [(17)2 - (15)2 ]
= (17 + 15) (17 - 15)
= 32 x 2
= 64 sq cm
Let a3 = Side of the third square.
According to the question, (a3)2 = 64 sq cm
∴ a3 = √64 = 8 cm
∴ Perimeter of the third square = 4 x a3 = 4 x 8 = 32 cm.