Answer:
84 m²
Explanation:
Solving : (Formula mentioned in question)
Finding area of base using Heron's Formula :
⇒ s = 5 + 4 + 3 / 2 = 12/2 = 6
⇒ s - a = 6 - 5 = 1
⇒ s - b = 6 - 4 = 2
⇒ s - c = 6 - 3 = 3
⇒ Area = √6 × 1 × 2 × 3
⇒ Area = √36 = 6 m²
Finding the Surface Area :
⇒ 2 × 6 + 12 × 6
⇒ 12 + 72
⇒ 84 m²