Correct Answer - Option 1 : 5.5 cm

**GIVEN:**

Increase in radius = 3 cm

Increase in surface area = 528 cm^{2}

**FORMULA USED:**

Surface area of sphere = 4πr^{2}

a^{2} - b^{2} = (a + b) (a - b)

**CALCULATION:**

Let original radius be r cm

∴ increased radius = (r + 3)cm

A.T.Q

4π(r + 3)^{2} - 4πr^{2} = 528

4π{(r + 3)2 - r^{2}} = 528

(r + 3 - r) (r + 3 + r) = (528/4) × (7/22)

(2r + 3) = 14

r = 11/2 = 5.5 cm

**∴ The radius was 5.5 cm**