Puzzles

What is the missing number? 

( ) - 2 = 4 

Well, the answer is 6, right? Because 6-2 = 4. 

Well, we do not use Algebra voids or parentheses but use a letter (usually an x or y). Then we write: 

x - 2 = 4 

It's that simple. The letter (in this case x) just means "do not know" and is frequently called unknown or variable. 

And once you solve it you write: 

x = 6 

Why use a letter? 
 
Because: 
is easier to write "x" to type parentheses (and easier to say "x" to "bracket or parentheses") 
If there are many parentheses (many "unknowns") we could use a different one for each letter.

By this I mean that algebra can be applied in different ways, both complex things and not so complex things, that not only the university and beyond know about algebra, but before we know it we have already begun to use.