A hedge fund's portfolio manager is employing the Merton model to estimate the volatility of a non-dividend-paying firm, whose equity is held within the fund's investment portfolio. Following a thorough investigation into the company, the manager has compiled the following information:

• Value of equity: USD 45 million
• Value of the firm's sole debt due in 5 years: USD 60 million
• $d1: 3.217790$
• $d2: 3.038905$

Assuming the firm's value has a constant volatility, what would be the calculated estimate of this volatility?