ate of return on the Samp;P 500 index was 23% for 2009, and the risk-free rate at the end of 2009 was 1%, calculate the equity risk premium for 2009?...

If the rate of return on the S&P 500 index was 23% for 2009, and the risk-free rate at the end of 2009 was 1%, calculate the equity risk premium for 2009? Recalculate the equity risk premium using 1981 data, when the risk free rate was 15% and the S&P 500 index return was minus 10%.