Confusing, isn't it?

Ah, how about like this:

You are to divide only aples by apples, oranges by oranges, etc.

Numbers by numbers, letters by letters.

3x / 12

Numbers by numbers:

3 / 12

= 1 / 4

Letters by letters:

x /....what? there is no x in the denomitor.

So you cannot divide x.

so leave it there in the numerator.

Hence,

3x / 12

= 1*x / 4

= x/4 -------------answer.

-------------------------------------------

8x / 4x

Numbers by numbers:

8 / 4 = 2

Letters by letters:

x / x = 1

So,

8x / 4x

= 2*1

= 2 ---------------answer.