4. (5 points) Suppose that you hold portfolio Time, which contains assets Past, Present and Future. Past's volatility is equal to 50%, Present has a volatility of 40%, and Future's volatility is equal to 30%. Suppose you invest 40% of your money in Past, and 30% each in Present and Future. a. Not knowing anything about the correlation between the three stocks, compute the highest possible volatility of portfolio Time. b. Let the volatility of portfolio Time be equal to the volatility in part (a), what can you conclude about the correlation between Past and Present