Ratio of base and perpendicular side of a right-angled triangle is 3:4 and its base is equal to the side of a square having area 81 cm². Find the perimeter of the triangle?

Side of the square=9 cm

Perpendicular side of the triangle= 12 cm

Hypotenuse of the triangle= $sqrt {81 + 144} = sqrt {225} =$ 15 cm

Perimeter of the triangle= 36 cm