Kl+kj factoring expression

The product of two negative rational numbers is always zero sometimes zero never zero

If f(x)=2x-6 and g(x)=3x+9, find (f-g)(x)

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?