Answer
The student combined the radicals incorrectly, since they were not like radicals.
Work Step by Step
In order to solve this problem, we may need to use the rules of radicals, which are listed on page 421. Once we have done this, we combine like radicals. Doing this, we find that the expression simplifies to:
$$2\sqrt[3]{10}+2\cdot \:3\sqrt[3]{5} \\ 2\left(\sqrt[3]{10}+3\sqrt[3]{5}\right)
$$
