The slope of the line below is 2. Use the coordinates of the labeled point to find a point-slope equation of the line

Find the value of the variable and the length of each secant segment.

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?  

Me. i can't figure out this question. give an explanation too. .