If x^2 + 1x^2 = 7, then the value of x^3 + 1x^3 where x > 0 is equal to:

Answer: Option A

$$\begin{array}{rl}& x^2+\frac{1}{x^2}=7\\ & x+\frac{1}{x}=3\\ & x^3+\frac{1}{x^3}=3^3-3\times 3=18\end{array}$$