If I understand it correctly:
a. One person would pay $8/month, the other only $5/month. (1) If you charge more than $8/month, you'll get nothing, because no one would pay it. (2) If you charge $8/month, you'll get $8, as only one person would pay that. (3) If you charge more than $5/month up to $8/month, you'll get the amount you charge from only one person - which is worse than the $8/month option in (2). However (4) if you charge $5/month, you'll get $10, since both people would pay it. Finally, (5) anyhting less than $5/month nets you less than $10/month, so it would be sub-optimal as well. So I'm thinking the answer is (4).
b. Can be calculated the same way as a., above.
c. can also be calculated like a., above. However, you would add the fees for the two services together when doing it.
I think d. and e. should fall out from doing the work for a-c above.
- Steve J