The perimeter of triangular field = 420m.Given that the ratios of the sides are 6 : 7 : 8.Sum of the ratios = 6 + 7 + 8 = 21Length of first side of the field = 621 × 420 = 6 × 20 = 120 mLength of second side of the field = 721 × 420 = 7 × 20 = 140 mLength of third side of the field = 821 × 420 = 8 × 20 = 160 mAccording to Heron′s formula the area (A) of triangle with sides a, b & c is given asA = 2√[s(s−a)(s−b)(s−c)]where 2s = (a+b+c).Here a = 120m , b = 140m , c = 160m , s = (120 + 140 + 160)2 = 4202 = 210 Area of triangular field = 2√[210 × (210 − 120)(210 − 140)(210 − 160)] = 2√(210 × 90 × 70 × 50) = √(3 × 7 × 3 × 3 × 7 × 5 × 10000) = 2√[(7 × 3 × 100 × 7 × 3 × 100) × 3 × 5] = 2100 2√15