The maths department of a college is trying to put on a fundraiser. The rent of the facility is $250.00 with $100.00 for electricity and $85.00 for miscellaneous expenses. The cost of producing each ticket is $9.00 and they will be priced at $14.00 each.

Cost function is basically your slope-intercept form: y = mx + b, but rewritten as a cost function C(x). Your book may or may not be changing the m & b, but I'll change them so you can see how it works:

C(x) = vx + f

Where x = the number of "units," in this case ticket sales. The equation is set up so that you can plug in any x you want and see what the total costs would add up to.

Where v = variable costs. That is, those costs which you will have for each ticket sold. If you sell one, you'd have 1 as x and have to count those costs once. If you sold 10, you'd have 10 as x and have to count those costs 10 times. Etc. Variable changes as you change x, the volume of tickets sold. (Hence vx.) Which costs do you have that are variable?

Where f = fixed costs. Those are the costs that will remain the same regardless of how many tickets you sell, as they remain fixed regardless. Which costs do you have which will remain fixed?