This will be 18.39, 6 is higher than 5, so the 8 is going higher so it's a 9 and you will get 18.39
The probabilities of knocking down zero, one, and two pins are

and

, respectively. The total probability of knocking down at most two is thus

, or

.
( x-5 ) (x + 6 )
multiply
X times X + 6x - 5x - 5 times 6
connect like terms
x squared + 6x - 5x - 30
Answer is
x squared + x - 30
C. You'd be starting at a higher floor (positive number) and descending floors (negative number per x). If you assume x is time it's a little more logical and visual.