Answer
The vertical asymptote is whatever value would get you a 0 in the denominator. since the second term in the denominator is -36, the first term would have to be 36 in order to make it 0. The only value that you could plug into the denominator at x to make it 6 is sqrt 6. (sqrt 6 )^2 x 6 = 36. 36 - 36 = 0, which is how you get the vertical denominator
x would be the negative value of the denominator value