The value of x would be: 5
So the number of pencils bought can be represented by an equation:

, where n is the number of notebooks bought. Since Helen bought 5 notebooks, simply plug 5 into n:

. So Helen bought 12 pencils.
The letter "x" is often used in algebra to mean a value that is not yet known. It is called a "variable" or sometimes an "unknown". In x + 2 = 7, x is a variable, but we can work out its value if we try!
200,000 is ten times 20,000