a)
The word "book" has 4 letters where 'o' is repeated twice. The formula to find the number of permutations of letters where some letters are repeated is
\frac{n!}{k_1! \cdot k_2! \cdot \ldots \cdot k_r!}
For "book":
\frac{4!}{2!} = \frac{24}{2} = 12
So, the number of different words that can be formed with the letters of "book" is 12.
b)
The word "cone" has 4 letters and all letters are distinct. The formula to find the number of permutations when all letters are distinct is:
n!
For "cone":
4! = 24
So, the number of different words that can be formed with the letters of "cone" is 24.