Answer:
13.70%
Explanation:
The expected return of a portfolio is said to be the weighted average of the returns of the individual components,
Given that:
Stock A has an expected return = 17.8%
Stock B has an expected return = 9.6%
the risk of Stock A as measured by its variance is 3 times that of Stock B. 
 If the two stocks are combined equally in a portfolio;
 Then :
The weight of both stocks will be 50% : 50 %
So the  portfolio's expected return can be determined as follows:
Expected return for stock A  = 50% × 17.8% 
Expected return = 0.50 × 17.8%
Expected return = 8.9 % 
Expected return for stock B = 50 % × 9.6 %
Expected return for stock B = 0.50 × 9.6%
Expected return for stock B = 4.8%
Expected return of the portfolio = summation of the expected return for both stocks
Expected return of the portfolio = 8.9 %  + 4.8%
Expected return of the portfolio =  13.70%