How do you solve a equation with one variable?

Basically, the same way that you solve equations that have variables only on one side. The general idea is that you can add, subtract, multiply and divide both sides of the quantities by the same amount (as long as you don't multiply or divide by zero).

For example:

4x = 2x + 3

If you subtract 2x from both sides, you are left with:

2x = 3