4.15. For each of the six cases in exercise 4.14, ABCO wants to consider what would happen to the return variance of ABCO’s $4 billion in stock if it revised the relative investment proportions in the two remaining subsidiaries. In particular, for each of the six possible sell-off scenarios, what proportion of the $4 billion should be invested in the two remaining subsidiaries if ABCO were to minimize its variance? Assume that short sales are not permitted.