Multiply numerator and denominator of the given function by 3-√6:
3-√6 5 5(3-√6) 5(3-√6)
--------- * ----------- = ------------ = ------------------
3-√6 3+√6 9 - 6 3
That's gonna be choice B:
[tex] \dfrac{5}{3-\sqrt6} \cdot \dfrac{3+\sqrt 6}{3+\sqrt 6} = \dfrac{ \textrm{something} }{3^2-6} = \dfrac{ \textrm{something} }{3}[/tex]
