Exercise 1 Page 44

To solve for z we need to isolate it by subtracting 3 from both sides of the equation. We want to subtract because addition and subtraction are inverse operations - they cancel each other out. This is allowed by the Subtraction Property of Equality.

We will check our solution by substituting this result back into the original equation and simplifying. If doing so results in an identity, our solution is correct.

An identity occurs when the left-hand side and the right-hand side of an equation are equal to one another. Since substituting z=-9 resulted in an identity, our solution is correct.