The 'x' stands for some number. We don't know which number, but that doesn't matter. Whatever we say about x works with any number.
For example, we say
"3x/3 = x".
What happens if x=1. Is this true? 3*1/3 is just 1 again, so yes it works!
What happens if x=5. Is this true? 3*5/3 is just 5 again, so yes it works!
What multiplication _means_ is having multiple copies. And what division _means_ is reversing multiplication --- dividing a pie into equal pieces and eating all but one of them.
If you have something, and you copies of it so that there are three in total --- say that 'x=chair', so that 3x=3 chairs. Then you divide the furniture into three equal groups. One natural way would be to divide it into three groups each with a single chair. Then you eat all of them but one. You're left with a single chair, which is what you started with! (and a full, splintery stomach)