Sorry, your answers are wrong . . .
(a) How many different strings can be formed by rearranging all the letters
of the word MISSISSAUGA?
There are 11 letters: .
There are: . possible strings.
(b) How many of the rearrangements in part (a) contain 4 Sís in a row?
Tape the four S's together.
Then we have 8 "letters" to arrange: .
There are: . arrangements.