Simplify. (Please provide explanation)

Answer:
[tex] 6 \sqrt[3]{3} [/tex]
Step-by-step explanation:
[tex] - \sqrt[3]{24} + 3 \sqrt[3]{81} [/tex]
[tex] - \sqrt[3]{2 \times 2 \times 2 \times 3} + 3 \sqrt[3]{3 \times 3 \times 3 \times 3} [/tex]
[tex] - 2 \sqrt[3]{3} + 3 \times 3 \sqrt[3]{3} [/tex]
[tex] - 3 \sqrt[3]{3} + 9 \sqrt[3]{3} [/tex]
[tex] - 3 + 9 \sqrt[3]{3} [/tex]
[tex]6 \sqrt[3]{3} [/tex]