Answer
$C(10,1)*C(9,1)*C(8,1)*C(7,1)*C(6,2)*C(4,4)$
Work Step by Step
We have to find the total number of sequences that can be formed using the letters of the word Casablanca.
It has 10 letters. (1s,1b,1l,1n,2c,4a)
The total number of 10-letter sequences of those letters is $C(10,1)*C(9,1)*C(8,1)*C(7,1)*C(6,2)*C(4,4)$
Because first we choose where to put the s in the sequence, then the b, (we can't put it where the s is, and we go on like that with every letter.