Algebra is a branch of mathematics in which letters such as \(x\) and \(y\) or other symbols are used to denote unknown quantities, and expressions are manipulated according to a set of rules.

In the picture, the unknown value \(x\) is balanced against a stack of \(6\) blocks, so \(x\) must be equal to \(6\) blocks.

Let's try an example of doing some algebra. We want to find the unknown value (or variable) \(x\) if \(x - 2 = 9\).

The value of \(x\) can be found by adding \(2\) to both sides of the equal sign like this:

Start with: \(x - 2 = 9\)

Add \(2\) to both sides: \(x - 2 + 2 = 9 + 2\).

Calculate: \(x + 0 = 11\).

The answer is \(x = 11\).