Push back on an unrealistic deadline or added scope

Help me push back on a request at work without just saying no. The request: [What was asked] From: [Who asked] Why it doesn't fit: [The constraint] Write a reply as a [Format] that: 1. Acknowledges what they need and why it matters. 2. States the constraint plainly, without hedging or over-apologizing. 3. Offers two or three real alternatives, such as a later date, a smaller first version, or dropping something else, with the cost of each. 4. Ends by asking them to choose. Keep it under 200 words. Then, separately, list anything I should confirm before sending it.