Stanford2012 has explained the solution perfectly.
The only thing I want to highlight here is the concept.
Let's say you have a fixed sum of $100 that needs to be distributed among 5 people. If you want to maximize one person's share, you need to give everyone else the minimum that you can. e.g. the question says each person must receive at least $10, what is the maximum one person can receive?
Since you want to maximize one person's share, you should give everyone else the minimum possible i.e. $ 10. You give $10 to each of the other 4 people and are left with $60, the maximum that you can give to one guy.
Similarly, if you want to minimize someone's share, you should give everyone else the maximum possible.
In your question here, a fixed amount has to be distributed among 6 people and one person's minimum share needs to be found. A person will receive minimum (say $x) , when everyone else gets the maximum that they can (that will be $6x/5).
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