It is given that there are 17 chairs all in all. In order to determine the possible arrangement for the 11 passengers we use the concept of basic principle of counting,
17 x 16 x 15 x 14 x 13 x ... x (17 - 11)
The answer to this item is 4.94 x 10^11
If five people are to sit in the back row, we take that 5 people as one group such that,
(5!)(12 x 11 x 10 x 9 x 8 x 7) = 79833600 ways