Given: A hollow cylinder of height 3 cm is melted and cast into a solid cylinder of height 9 cm he outer radius and inner radius of the hollow cylinder are 4.3 cm and 1.1 cm Formula used: Volume of solid cylinder = πr2h Volume of hollow cylinder = πR2h - πr2h = πh(R2 - r2) Total surface area = 2πr(h + r) Calculation: let the solid cylinder radius be x. Volume of hollow cylinder = πh(R2 - r2) ⇒ π3 ⇒ π3(5.4 × 3.2) ----(1) Volume of solid cylinder = πx29 ----(2) From equation(1) and equation(2); π3(5.4 × 3.2) = πx29 ⇒ x2 = (18 × 32)/100 = 576/100 ⇒ x2 = (24/10)2 ⇒ x = 2.4 Total surface area = 2πr(h + r) ⇒ 2 × π × 2.4(2.4 + 9) ⇒ 2 × π × 2.4 × 11.4 ⇒ 54.72 π cm2 ∴ The total surface area (in cm2) of the solid cylinder is 54.72 π cm2.