Simplify:

$\displaystyle 6\sqrt{44}+4\sqrt{120}-\sqrt{99}-3\sqrt{120}$

$\displaystyle 12\sqrt{11}+8\sqrt{30}-3\sqrt{11}-3\sqrt{30}$

$\displaystyle 9\sqrt{11}+5\sqrt{30} \ \ \ \ \ \ \ \text{:my answer}$

$\displaystyle 9\sqrt{11}+\sqrt{30} \ \ \ \ \ \ \ \ \text{:text book answer}$

Where have I gone wrong!

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