\[\left( \sqrt[3]{x} \right)^{3} + \left( \sqrt[3]{3} \right)^{3} = 15 - \sqrt{x}\]
\[x + 3 = 15 - \sqrt{x}\]
\[x + \sqrt{x} + 3 - 15 = 0\]
\[t = \sqrt{x};\ \ \ \ t \geq 0\]
\[t^{2} + t - 12 = 0\]
\[t_{1} = 3;\ \ \ \ \]
\[t_{2} = - 4\ (не\ подходит).\]
\[\sqrt{x} = 3 \Longrightarrow x = 9.\]
\[Ответ:x = 9.\]