1. Let's state the problem: Solve part 4 as done previously. 2. Since the user refers to "part 4" without context, we assume it is a continuation of a previous problem involving algebraic or arithmetic operations. 3. To solve part 4, we need the exact problem statement or expression. Without it, we cannot proceed. 4. Please provide the details of part 4 so we can solve it step-by-step as before.