Chapter 2 - Solving Equations - 2-1 Solving One-Step Equations - Lesson Check - Page 85: 7

$x = 13$

$x - 4 = 9$ In this equation, we need to isolate $x$ by adding the constant 4 to both sides of the equation so as to join the constants on the other side of the equation and eliminate them from the left hand side. This is as shown below: $x - 4 + 4 = 9 + 4$ Simplifying the equation by joining like terms together, we have: $x = 13$