Company NothingOrAll (NOA) is known to be undertaking a new project. If the project is successful the value of the firm's debt and equity in a year will be $52 million, if it is unsuccessful the firm's value will be $28 million. NOA has a zero bond issue outstanding, which is due in one year with face value $40 million. The risk-free interest rate is 5%. NOA's current value of debt and equity is $40 million.

What is the value of risk-free debt (in million $), i.e., since the debt of the company is risky by how much is its value lower compared to risk-free debt?