Y=-7+2x how do i answer this problem correctly

Aschool puts on a play. the play costs $1,200 in expenses. the students charge $4.00 for tickets. there will be one performance of the play in an auditorium that seats 500 people. what is the domain of the function that shows the profit as a function of the number of tickets sold?  

F(n + 1) = f(n) – 8. if f(1) = 100, what is f(6)?

The radius of the earth is two times the radius of the moon. what fraction of the volume of the earth is the volume of the moon?