CAPM – debt beta

Hi sir,

This question is from your revision notes.

If market return is 10% and risk rate is 5%, what is the required rate of return on debt which has a debt beta of 0.3? What is the cost of debt to the company if the tax rate is 33%?

Answer:
Required return = 5% + 0.37 (10%-5%) = 6.85%
Cost of debt = 6.85% X (1-0.33) = 4.59%

Could you please explain where the 0.37 came from? Would be greatly appreciated.

Kind regards,
Yazan