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 2000 + (- 6000) = - 4000.

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. 2000 + x = - 4000).

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:

- 5000 + x = 4000

- 5000 + x + 5000 = 4000 + 5000

0 + x = 9000

x = 9000

Check the answer by substituting the answer (9000) back into the equation.

- 5000 + 9000 = 4000