4. please help me with this

The table below shows interest rates and bond ratings on long-term bonds of equal maturity collected from an old February 2005 copy of the Wall Street Journal. In 2005 the default risk premium on AAA. AA. A. and BBB corporate bonds were, respectively: 4.65%; 0.80%; 1.13%; 1.75% 0.80%; 0.15%; 0.18%; 0.56% 0.89%; 1.04%; 1.22%; 1.78% 0.95%; 0.33%; 0.74%; 1.25% 1.00%; 1.25%; 1.30%; 1.50%