This is a pretty easy problem you can look at A as adding all the cases subtracting the E[x] (where x is the breifcases) and then divided by 4 (due to there only being 4 cases left).

for b all you really have to do is find E[x] and times it by .7 because we know since the taxes is a constant we can evaluate it during the summation or after the summation (and it is easier and faster to do it afterwards).

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Abstract algebra continues the conceptual developments of linear algebra, on an even grander scale.

Dr. Paul Garrett