Answer: B.
Explanation:
You can rationalize a denominator by multiplying both the numerator and denominator by the radical in the denominator. In this case, it is the square root of 6.
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The square root of 6 multiplied by the square root of 6 is equal to 6, so you can simplify the equation to this:

You can multiply simplified radicals together. First, check that 3 and 6 are simplified (their multiples do not include squares. If 8 was in one of the radicals, it could be simplified to 2*square root of 2.)

Because 18 can be simplified to 9 * 2, and 9 is a square of 3, you can simplify this to
.
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