$5.($a$)$ How many permutations are there of the letters of the word "abracadabra"?$($b$)$ How many permutations if the first letter must be $\text{'}$a$\text{'}$ and the last letter $\text{'}$b$\text{'}?($c$)$ How many permutations are there such that the first letter is $\text{'}$a$\text{'}$ or the last letter is $\text{'}$b$\text{'}?$