In this case, we'll have to carry out several steps to find the solution.
Step 01:
Data:
[tex]21\sqrt[3]{15}-9\sqrt[3]{15}[/tex]
Step 02:
radical functions:
[tex]21\sqrt[3]{15}-9\sqrt[3]{15}=12\sqrt[3]{15}[/tex]
The answer is:
[tex]12\sqrt[3]{15}[/tex]
