You can easily do that by doing cross multiplication.
So, any whole number can be a fraction by adding 1 over them, right?
Cross multiply 1/3 x 9/1.
You would cancel the denominator of 1/3, which is 3, to 1. Then cancel the numerator of 9/1, which is 9, to 3 because 9 divided by 3 is 3.
Now, you're left with 1/1 x 3/1. Simplify.
The answer is 3/1 or 3.
I hope this answer is helpful! :)