When we multiple a number by a fraction we first multiply the numerators and then multiple the denominators. In this sense multiplying a fraction like 3 x 3/4 is fairly easy.
The trick is to convert 3 to 3/1 so we have a fraction. Since we are dividing by "1" we haven't change the value, just the way it is written. We then have:
3/1 x 3/4
We multiply the numerators: 3 x 3 = 9
and then the denominators: 1 x 4 = 4
We end up with 9/4 which we also change to the mixed number 2 1/4.