Using CAPM, find the equity betas only, everything, companies, average

smartpants

Based on CAPM and using the returns on the market portfolio and the risk-free rates, estimate the equity betas for the two companies A and B.

If I keep it simple and use only three months,

so return for A are:
-10.91%
6.52%
-3.74%

returns for B are:
1.13%
3.85%
10.11%

S&P 500 returns:
7.04%
4.99%
0.91%

and risk free rate is:
0.43%
0.39%
0.39%

I know I need to use the CAPM formula but I don't whether to average everything, or calculate the equity betas one by one and then average that, it's baffling