Correct Answer - Option 3 : 1,320 cm

2
**Given:**

Inner diameter of hollow cylindrical pipe = 8 cm

Outer diameter = 12 cm

Height of cylinder (h) = 21 cm

**Concepts used:**

CSA of hollow cylinder = 2π × (r + R) × h

**Calculation:**

Inner radius (r) of cylindrical pipe = ½ × Inner diameter of cylinder = 8/2 cm = 4 cm

Outer radius (R) of cylinder = ½ × Outer diameter of cylinder = 12/2 cm = 6 cm

CSA of hollow cylindrical pipe = 2 × 22/7 × (4 + 6) × 21 cm^{2}

⇒ CSA = 1,320 cm^{2}

**∴ CSA of hollow cylindrical pipe is equal to 1,320 cm**^{2}.