Pre-Algebra Practice Questions: Isolating x in an Equation

By Mark Zegarelli

You can solve algebraic equations by isolating x—that is, by getting x alone on one side of the equation and everything else on the other side. For most basic equations, isolating x involves a few steps, as you’ll see in the following practice questions.

Practice questions

  1. Find the value of x in the equation 9x – 2 = 6x + 7.
  2. Find the value of x in 4x – 17 = x + 22.

Answers and explanations

  1. x = 3

    First, add or subtract the same number from each side to get all constants (non-x terms) on one side of the equation. In this example, you want to get all constants on the right side of the equation, so you add 2 to both sides:

    PREALGEBRA_3101

    Second, you add or subtract to get all x terms on the other side of the equation. Here, you want to get all x terms on the left side, so you subtract 6x from both sides:

    PREALGEBRA_3102

    Third, you divide by 3 to isolate x:

    PREALGEBRA_3103

  2. x = 13

    Start by adding or subtracting the same number from each side to get all constants (non-x terms) on one side of the equation. Here, you add 17 to both sides to get all constants on the right side of the equation:

    PREALGEBRA_3104

    The second step is to add or subtract to get all x terms on the other side of the equation. In this example, you need to subtract x from both sides to get all x terms on the left side:

    PREALGEBRA_3105

    The third step is to divide (in this case, by 3) to isolate x:

    PREALGEBRA_3106