Chapter 2 - Solving Equations - 2-2 Solving Two-Step Equations - Practice and Problem-Solving Exercises - Page 93: 72

$z=6.5$

In order to solve this algebraic expression, we must isolate the variable. A variable is the letter in the problem (for instance, in the equation x+2=10, x is the variable). Because addition and subtraction are inverse operations (they cancel each other out), we know we must add when a number is being subtracted from the variable and subtract when a number is being added to the variable. In the equation $z-2=4.5$, we must get rid of the 2, which is on the same side as z, in order to solve. Thus, we add 2 on both sides of the equation to find that $z=6.5$.