6.061. $2 \sqrt[3]{x}+5 \sqrt[6]{x}-18=0$.
## Solution.

Domain of definition: $x \geq 0$.

Let $\sqrt[6]{x}=y \geq 0$. The equation in terms of $y$ becomes $2 y^{2}+5 y-18=0$, from which we find $y_{1}=-\frac{9}{2}, y_{2}=2 ; y_{1}=-\frac{9}{2}<0$ is not valid.

Then $\sqrt[6]{x}=2, x=2^{6}=64$.

Answer: $x=64$.