Saying 3/4 * 3 is the same thing as saying 3/4 of 3. Imagine you have 3 pies, each cut into 4 slices. That would be 3 * 4 = 12 slices of pie, right?
So when there's 12 slices, that would be 4/4 of the pies, since all the pieces are there.
To find out how many pies we would have with 3/4 of the pie left, we just need to multiply the original equation.
3 * 3/4 = 2 1/4
The product of those two numbers lies between 2 and 3.
Hope that helped =)