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 + 2 = 4.

One of the terms in an equation may not be known and needs to be determined. The unknown term may be represented by a letter such as x (e.g. 2 + x = 4). The equation is solved by finding the value of the unknown x that makes the two sides of the equation have the same value.

Use the subtractive equation property to find the value of x in addition equations. The subtractive equation property states that the two sides of an equation remain equal if the same number is subtracted from each side.

Example:

5 + x = 12
5 + x - 5 = 12 - 5
0 + x = 7
x = 7

Check the answer by substituting (7) for x in the original equation. The answer is correct if the expressions on each side of the equals sign have the same value.

5 + 7 = 12