How do you do prime factorization. i still dont get it.

Prime factorization is simply making a number become simplified in the smallest term it can be in. For example 9 Can be broken down into 3 times 3. Your prime numbers are 2, 3, 5, 7, 11, 13, 17,19 because nothing times something will give you that number besides itself and 1

First you divide 39/40
you would get 0.975