Fundamental CAPM questions

A couple questions about the CAPM model:

1. 
   

   If I only know the riskfree rate and expected market return, how do I solve for $\beta$ ?

   
   


2. 
   
   

   Given the stock's variance, how do I solve the percentage of it that is due to market risk and how do I interpret this?

   
   

I searched this question through google, but I cannot find reasonable answer. Please help me! Thanks in advance for your help.