SD Portfolio, correct weights?

You are a portfolio manager, and your work is to analyse two stocks, Moo and Neh. You estimated the returns using the single index model and got the following results :
image

The standard deviations for the market index, Moo and Neh are 25% , 30%, and 45%, respec tively.

  1. What is the firm-specific risk for Moo and Neh, respectively?
  2. What are the covariance and correlation coefficient between the two stocks?
  3. What is the standard deviation of your portfolio if you invest 40% in Moo and 40% in Neh, and 20% in T-bill?

I get 1 to be 22,36% sd for moo and 24,87% for Neh
2 Cov=0,075 and corrP=0,55556
3. Should we take =(0,5^20,3^2)+(0,5^20,45^2)+20,50,50,30,45*0,556"=0,116 for SD portfolio? I mean, what about the t-bills then that we put in 20% as a weight? But, t-bills doesn’t account for SD so not sure if I should use weight as 50% for both stocks or 40% for both stocks?

Question from old cfa question bank 2008.