We are given that Mike has $36, if he spends 1/3 of this amount, the amount spent is the product of 36 and 1/3, that is:
Therefore, he spends $12 on the movie.
Now we are told that he spends 2/9 of the money, therefore, he spent:
In total, he spent $8 on the sandwich.
The money he has left is:
Therefore, he can't buy an $18 dollars book.