You probably are looking at maximizing the revenue, not profit
But here we go
Assuming all seats will be sold at the $5 price you would have a revenue of $6000
Revenue = (1200 - 100X) (5+.5X)
1200- 100X how many will attend for each 50 cent increase, X = 1 means 1 , 50 cent increase
5+.5X what each person will pay that attends
R(X) = (1200 - 100X)(5+ .5X) = 6000 + 100X - 50X^2
This is a quadratic opening down and has a maximum at it's vertex:
-b/2a
-100/(-100) = 1
The max occurs at X = 1, 1 50 cent increase
Therefore the ticket price they should charge should be $5.50
To graph the quadratic, you need to graph in the first quadrant with a y-int of (0,6000).
Then just plug in values of X into the quadratic above and plot points.
Make sure to plot (1, 6050) as this is the Maximum
When X = 12, no one is attending so make sure to plot that as your x-int.
