Step-by-step explanation:
It depends on the definition of "factor" that you use.
One dictionary defines "factor" to be ...
"a number or quantity that when multiplied with another produces a given number or expression"
In that sense, 7 can be a factor of 3, because 7 × (3/7) = 3.
___
Often we use the term "factor" when we mean "integer divisor", or "positive integer divisor". Using this last definition, the only factors of 3 are 1 and 3.
Other times, we use the term "factor" to mean "prime factor." By this definition, the only factor of 3 is 3 itself.