Capex request evaluation: ROI, payback, and approval memo

Evaluate a capex request for {project_name}.

Inputs:
- Capex amount and timing: {capex_timing}
- Expected benefits (cost savings/revenue): {benefits}
- Useful life and residual value: {useful_life_residual}
- Operating cost impacts: {opex_impacts}
- Discount rate / hurdle rate: {hurdle_rate}
- Strategic rationale: {strategic_rationale}

Output:
1) ROI metrics: NPV, IRR (if possible), payback period (show formulas).
2) Key assumptions and sensitivities (top 3).
3) Risks and mitigation actions.
4) Draft approval memo (1 page) with recommendation and conditions.