Correct Answer - Option 4 : 4.5 cm

**Given:**

⇒ Height of cylindrical pipe = 14cm

⇒ Volume of metal used = 99 cm

**Formula:**

Let r = radius of cylinder and h = height of cylinder

⇒ Volume of cylinder = πr^{2}h

⇒ Curved surface area of cylinder = 2πrh

**Calculation:**

⇒ 2πRh - 2πrh = 44

⇒ R - r = 0.5cm

Then,

⇒ πR^{2}h - πr^{2}h = 99

⇒ (R^{2} - r^{2}) = 2.25

⇒ (R + r)(R - r) = 2.25

**∴ (R + r) = 4.5**