A solid metal sphere of radius 21 cm is cut into two identical hemispheres. What is the combined total surface area of the two hemispheres, in square cm? (Use π = 22/7.)

Here π$r^2=(22/7)\times 441=1386$ sq cm. Each solid hemisphere has a curved part 2π$r^2$ plus a flat circular face π$r^2$, i.e. 3π$r^2=4158$ sq cm, so the two together give 6π$r^2=8316$ sq cm. The trap 5544 is the sphere's own surface 4π$r^2$, which ignores that cutting exposes two new circular faces; 4158 gives only one hemisphere; 2772 is the pair of new flat faces alone, 2π$r^2$, the increase rather than the total.