Given: ratio of sides of a triangle = 5 : 4 : 3 perimeter of the triangle = 84 cm Formula used: Perimeter of triangle = Sum of sides Calculations: Let the sides of triangle be 5x, 4x and 3x so that they are in ratio 5 : 4 : 3. ∴5x+4x+3x=84 ⇒ 12x = 84 ⇒ x = 7 cm So, the sides of triangles are 35, 28 and 21 meters. ∴ The length of the largest side is 35 m.