Answer: C
\[ (x + y) = 3 + \sqrt{8} + 3 - \sqrt{8} = 6 \] \[ xy = (3 + \sqrt{8})(3 - \sqrt{8}) = 9 - 8 = 1 \] \[ x^{-3} + y^{-3} = \frac{1}{x^3} + \frac{1}{y^3} = \frac{y^3 + x^3}{x^3 y^3} = \frac{(x + y)^3 - 3xy(x + y)}{(xy)^3} \] \[ = \frac{6^3 - 3 \times 1 \times 6}{1^3} = \frac{216 - 18}{1} = 198 \]
\[ (x + y) = 3 + \sqrt{8} + 3 - \sqrt{8} = 6 \] \[ xy = (3 + \sqrt{8})(3 - \sqrt{8}) = 9 - 8 = 1 \] \[ x^{-3} + y^{-3} = \frac{1}{x^3} + \frac{1}{y^3} = \frac{y^3 + x^3}{x^3 y^3} = \frac{(x + y)^3 - 3xy(x + y)}{(xy)^3} \] \[ = \frac{6^3 - 3 \times 1 \times 6}{1^3} = \frac{216 - 18}{1} = 198 \]