An equation is a mathematical statement such that the expression on the left
side of the equals sign (=) has the same value as the expression on the right side.
An example of an equation is 600 - 400 = 200.

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. x - 400 = 200).

The solution of an equation is finding the value of the unknown x. To find the
value of x we can 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:

x - 500 = 700

x - 500 + 500 = 700 + 500

x - 0 = 1200

x = 1200

Check the answer by substituting the value of x (1200) back into the equation.

1200 - 500 = 700