Determine whether a number is a solution

1. Determine the left side (1)
2. Determine the right side (2)
3. The letter x is the variable (or the (3))

1. (1) 6 + 3 = 9
2. (2) 2 + 4 = 7
3. (3) x + 5 = 15

A number that makes an equation true when substituted for the variable is called a (1) and it is said to (2) the equation.