A hollow hemi-spherical vessel of steel of 0.5 cm thick and twice of its internal radius is 24cm. Then find the value of total surface area (in cm2) of the vessel?

Internal radius r = 12 cm, thickness = 0.5 cm, so external radius R = 12.5 cm. For hollow hemisphere: Total surface area = Outer curved surface + Inner curved surface + Ring area at top = 2πR² + 2πr² + π(R² - r²) = 2π(12.5)² + 2π(12)² + π((12.5)² - 12²) = 2π(156.25) + 2π(144) + π(156.25 - 144) = 312.5π + 288π + 12.25π = 612.75π cm².