The prime factors of 75 are 3 and 5. A prime factor is any factor of a number that is also a prime number. A prime number is a designation for numbers that only have two factors: 1 and themselves.
The first step in identifying prime factors of a number is to determine all the factors of that number. To do so, divide the number by all the numbers leading up to it. Record all numbers where there is no remainder after the division. For 75, the factors are 1, 3, 5, 15, 25 and 75. Of those numbers, the only prime numbers are 3 and 5.