Answer:
a) A = 4.50% and B = 2.00% 
b) SD for A = 4.15 %
c) Portfolio Return = 3.0%
Explanation:
a) Expected Returns for Both A and B respectively:
In order to calculate the expected returns, let's categorize the given data first.
Economy        Probability      Stock A       Stock B
Booming            0.30               10%               20%
Neutral               0.30                5%                 0%
Recession          0.40                 0%                -10% (not 10%) 
So, 
Expected Return for Stock A:
A =   Sum of (all Probability x Stock A)
A = (0.30 x 0.10) + (0.30 x 0.05) + (0.40 x 0.00) 
A = 0.045
<u><em>A = 4.50 % </em></u>
Return for Stock B:
B = Sum of all Probability x Stock B
B = (0.30 x 0.20) + (0.30 x 0.00) + (0.40 x -0.10) 
B = 0.002 
<u>B = 2.0%</u>  
<em>b) Standard Deviation /Risk for Stock A:</em>
SD for A = Sum (Square Root (Probability*(Stock A Return - Expected Return of Stock A)²) )
SD for A = 
SD for A = 0.0415
<u><em>SD for A = 4.15%</em></u>
c) Portfolio Return Given that:
                                         Value          Weight         Return 
Stock A                          4000              0.4               4.50%
Stock B                          6000             0.6                 2.0% 
                                       10000
Portfolio Return =  Sum of ( Weight x Return) 
                           = (0.4 x 0.045) + (0.6 x 0.02)
                           = 0.03
<em><u>Portfolio Return = 3%</u></em>