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 60 - 40 = 20.

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 - 40 = 20).

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 - 50 = 70

x - 50 + 50 = 70 + 50

x - 0 = 120

x = 120

Check the answer by substituting the value of x (120) back into the equation.

120 - 50 = 70