My company charges 10 cents per minute over 5 minutes when using internet at its store. it also charges a 5 dollar fee for usage. how many minutes can i get with 10 dollars?

So if you use it for less than 5 minutes is more than likely free.

now, you start downloading the macarena song and other mp3s, and it takes longer then they charge 10 cents or $0.10  per minute after those 5 minutes.

so, if you use it 

6 mins   you pay 1 * 0.10
7 mins   you pay 2 * 0.10
8 mins   you pay 3 * 0.10
9 mins   you pay 4 * 0.10
10 mins   you pay 5 * 0.10

x mins   you pay (x - 5) * 0.10   so long "x" is 5 or higher.

now, they charge a $5 fee, that's just a connection fee, so is charged only once,

so the cost function will be

It will might be false