A factor is just a number that evenly divides another number.
- 3 is a factor of 15 because $$ 15 \div 3 $$ is an whole number (5)
- 6 is a factor of 18 because $$ 18 \div 6 $$ is an whole number (3)
- 5 is a factor of 15 because $$ 15 \div 5 $$ is an whole number (3)
- 2 is a factor of 12 because $$ 12 \div 2 $$ is an whole number (6)
- 3 is not a factor of 14 because $$ 14 \div 3 $$ is not a whole number
- 6 is not a factor of 22 because $$ 22 \div 6 $$ is not a whole number