The internal and external radius of a hollow hemispherical vessel are 7 cm and 8 cm respectively. What is total surface area of the vessel?

756.74 cm²

T.S.A. = C.S.A. of (inner + outer) hemispherical + area of ring

         = 2\(\pi \) (R² + r²) + \(\pi \) (R² - r²) 

         = 3\(\pi \) R² + \(\pi \) r²

         = \(\pi \) (3 × (8)² + (7)²)

         = 3.14 × 241 = 756.74 cm²