To find the greatest prime factor of 99, I need to factor 99 into its prime factors. One way to do this is to use a factor tree, where I start with 99 and break it down into two smaller factors, and then repeat the process until I reach only prime factors. For example, I can start by writing 99 as 9 times 11. Then, I can break down 9 as 3 times 3, and 11 is already prime. So, the prime factorization of 99 is 3 times 3 times 11. The greatest prime factor is the largest of these three numbers, which is 11. 
What is the greatest prime factor of 99?