An equation is a mathematical statement that has an expression on the left side of the equals sign (=) with the same value as the expression on the right side. An example of an equation is 2 + (- 6) = - 4.

One of the terms in an equation may not be know and needs to be determined. Often this unknown term is represented by a letter such as x. (e.g. 2 + x = - 4).

The solution of an equation is finding the value of the unknown x. To find the value of x we can use the subtractive equation property which says: "The two sides of an equation remain equal if the same number is subtracted from each side." We may also use the additive equation property which says: "The two sides of an equation remain equal if the same number is added to each side."

Example:
- 5 + x = 4
- 5 + x + 5 = 4 + 5
0 + x = 9
x = 9
Check the answer by substituting the answer (9) back into the equation.
- 5 + 9 = 4