Henry is trying to unlever a firm's common equity beta but is struggling to do so because he has been told by his boss that he is not allowed to assume a debt beta equal to zero. His firm insists on using a market risk premium of 6% in all of its analysis, and the current yield on long-term U.S. government bonds is 1.9%.     If the firm's cost of debt is 3%, what would be an appropriate debt beta to use for this firm?