Question 1080883
x-intercept is (18,0)
y-intercept is (0,90,000)


the slope is equal to (y2-y1)/(x2-x1)


if (x1,y1) = (18,0) and (x2,y2) = 0,90,000, then the slope is equal to (90,000-0) /(0-18) = 90,000/-18 = -5000.


the general form of a straight line equation is y = mx + b


m is the slope
b is the y-intercept


your equation becomes y = -5000 * x + b


replace x and y with the value of one of the points.


try (x1,y1) = (18,0)


the formuila becomes 0 = -5000 * 18 + b


solve for b to get b = 90,000


that should have been obvious because one of the points was the y-intercept.


stupid of me but i got the right answer anyway.


the equation becomes y = -5000 * x + 90,000


the graph shows the tickets available.


presumably, as tickets are sold, the number of available tickets becomes less.


after 18 hours, all the tickets are sold and there are no more tickets available.


that says that 90,000 tickets were sold in 18 hours.


the first question is how many tickets remain after 16 hours.


the equation of y = 90,000 - 5000 * x becomes y = 90,000 - 5000 * 16 which becomes y = 90,000 - 80,000 which becomes y = 10,000.


that means there are 10,000 tickets left after 16 hours.


the next question is how long does it take to sell the first 20,000 available seats.


since 5000 tickets are sold every hour, this means that the first 20,000 tickets were sold in 4 hours.


the graph looks like this:


<img src = "http://theo.x10hosting.com/2017/051208.jpg" alt="$$$" </>


you can see that, after 4 hours, 70,000 tickets are left, which means that 20,000 have been sold.