with a throw of 3 dice, what is the probability of getting a 9 or an 11?

The answer is 52/216

Here is the solution posted

I am having really great difficulty in understanding what all the table parameters mean. I also don't know how to get those values on the table. maybe you can guide me?

$\displaystyle S_{12}$ = sum of outcomes in dice 1 and dice 2

$\displaystyle P_{1\&2}$ = number of permutations in $\displaystyle S_{12} $

$\displaystyle O_3$ = outcome of dice 3 to make 9 or 11

$\displaystyle P_3$ = Number of permutations each of $\displaystyle O_3$

$\displaystyle P = (P_{1\&2})(P_{3}) $ = multiplying both

I have a background knowledge on permutation which is nPr where n = total ways , r = number of ways the total can be permutated