Can you please explain and solve the following questions. I do not understand how they got the answers which are highlighted in orange.

The next two questions are based on the following problem Consider the market with T-bills and risky securities A and B such that rf=2%, E(rA)=15%, OA=24%, E(B)=8%, OB=12%. The correlation coefficient between securities A and B is -1. Assume that short- selling is allowed. (5 MARKS) What are the expected return and the variance of the minimum variance portfolio A) 10.33% and 0% B) 12.67% and 0% C) 0% and 12% D) 10.33% and 12% E) None of the above ANSWER: A(2 MARKS) Consider an investor who is indifferent between stocks B and C and has the coefficient of risk aversion of 2. The standard deviation of stock B is 25% while expected returns of the stocks are E(B)=12% and E(rc)=8%. What should be the standard deviation of stock C? A) 15% B) cannot be determined UB = 25% E ( rB ) = 12% C) 33% D) 20% oc = ? E (re ) = 8.1. E) 10% ANSWER: A