Answer
$2\times2\times2\times2\times2\times2$
Work Step by Step
The first step is to write 64 at the top of your factor tree. The next question is what 2 numbers multiply together to get 64. For this example, I used 8 and 8. So, 8 and 8 are written under the 64 as 2 different "branches."
For each new number "branching" out from the previous number, you must determine if it is prime. 8 is not prime because 4 and 2 are another set of factors for 8 besides 8 itself. Now, 2 is prime, so circle the number 2 to show its separation from the rest of the factor tree. 4 is not prime because 2 and 2 are another set of factors for 4 besides 4 itself. Now, 2 and 2 are both prime, so circle each number separately.
Repeat this method for the second 8 under the original 64.
Looking at all 6 circled numbers, $2\times2\times2\times2\times2\times2$ would be the prime factorization for 64.
