1. **State the problem:** Evaluate the expression $15 - z^2$ when $z = 3$. 2. **Recall the order of operations (PEMDAS):** - Parentheses - Exponents - Multiplication and Division (from left to right) - Addition and Subtraction (from left to right) 3. **Substitute $z = 3$ into the expression:** $$15 - 3^2$$ 4. **Calculate the exponent first:** $$3^2 = 9$$ 5. **Rewrite the expression with the calculated exponent:** $$15 - 9$$ 6. **Perform the subtraction:** $$15 - 9 = 6$$ **Final answer:** $$6$$