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 22 + 22 = 44.

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. 22 + x = 44). 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:
50 + x = 120
50 + x - 50 = 120 - 50
0 + x = 70
x = 70
Check the answer by substituting (70) for x in the original equation. The answer is correct if the expressions on each side of the equals sign have the same value.
50 + 70 = 120