Let’s work through this step-by-step.

**1. Industry and business risk profile**  
Bouygues is a diversified industrial group (construction, media, telecoms), not a regulated utility, pure E&P, or transportation infrastructure company. Its main segments—construction and telecoms—are competitive and cyclical, placing it in the “standard volatility” category for financial ratio benchmarks under S&P’s methodology.

**2. Financial position and leverage**  
- **Equity** (Dec 2022): €13,932m  
- **Net debt** (Dec 2022): €7,440m, up sharply from €941m a year earlier—this is largely due to the acquisition of Equans.  
- **Leverage (net debt/equity)** moved from very low to around 53%, which for a non-utility, cyclical group signals a material increase in credit risk.  
- **Fully adjusted debt** would also include leases and pension obligations, further increasing leverage.

**3. Profitability and cash flow**  
- Revenue grew significantly (mainly M&A-driven).  
- Operating profit from recurring activities was €1,962m, but total profit attributable to owners declined to €973m from €1,125m.  
- Cash flow from operations remains solid at ~€3bn, but capex and acquisition outflows have reduced free cash flow.

**4. Hybrid issuance context**  
- The current capital structure shows no outstanding hybrids.  
- The sharp increase in debt to fund the Equans acquisition suggests moderate rating headroom pressure, especially if Bouygues wants to maintain its strong investment-grade rating.  
- The cost of hybrid debt in 2022 (sub-senior delta ~2.3%) was materially above the corporate IG average, making hybrid issuance noticeably more expensive than senior debt.

**5. Application of guidance**  
- The large acquisition already executed means refinancing needs are not “very high” now, but leverage moved from extremely conservative to moderate.  
- This points away from 0% (there is some rationale for leverage optimization) but also away from 11.25% or 15% (no transformational capex pipeline announced beyond what’s already funded, and cost is high relative to senior debt).  
- Given no existing hybrids, a moderate placement of **3.75%** would provide some rating flexibility without materially increasing the group’s overall cost of debt.  
- €13,932m equity + €7,440m net debt = ~€21.4bn total adjusted capital (simplified). 3.75% would equal ~€800m, easily within annual market capacity.

**Final answer:**

<answer>3.75%</answer>