Find the surface area of a frustum of cone, whose larger and smaller radius is $12$ cm and $8$ cm. The height of the cone is $3$ cm. (Use $\pi = 3$)

First, the slant height of the frustum is calculated using the Pythagorean theorem with the height and the difference of the radii, so the slant height is the square root of 3 squared plus the square of (12 minus 8), which equals 5 cm. The total surface area formula is pi times the sum of the radii times the slant height plus pi times R squared plus pi times r squared. Substituting the values gives 3 times (12 plus 8) times 5 plus 3 times 12 squared plus 3 times 8 squared, which simplifies to 300 plus 432 plus 192. The total surface area is 924 square centimeters.

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