1. Let's clarify the problem: you want a brief explanation of the logic behind the solution to part d. 2. The key is to identify what the problem asks and the main principle or formula used. 3. Usually, part d builds on previous parts, so understanding the earlier steps helps. 4. The logic often involves applying a formula, substituting known values, and simplifying. 5. For example, if part d involves solving for a variable, the logic is isolating that variable step-by-step. 6. Think of it as breaking down the problem into smaller, manageable pieces and solving each piece logically. 7. If you provide the exact problem or part d, I can give a more specific brief explanation.