1. Let's start by stating the problem: Solve the equation or expression labeled as number 4. Since the user did not provide the exact problem, please provide the full problem statement for number 4 so I can assist you properly. 2. Generally, to solve a math problem, we identify the type (e.g., algebraic equation, quadratic, system of equations) and apply the relevant formulas or methods. 3. Once the problem is provided, I will show the formula used, explain important rules, and demonstrate all intermediate steps clearly. Please provide the full text or equation of number 4 so I can help you solve it step-by-step.