Factors are like the numbers that can be multiplied by other numbers to get a certain number. In this case, you're trying to find factors of 16 so for example:
4*4=16 which makes 4 a factor of 16.
Here are the rest of the factors:
2*8=16
1*16=16
When listing factors, most teachers want you to put them in numerical order
So all the factors of 16 would be 1, 2, 4, 8, and 16
