Question 896244
The $7 is the fixed cost. It does not change based on how many tickets you buy. 


The $2 is known as the variable cost. It changes based on how many ticket books you buy.


Let b = number of ticket books bought


If it costs $7 to get in the door, and $2 per book, then it costs 7 + 2b or 2b + 7 dollars total. This is the sum of the fixed cost and variable cost.


This total cost is equal to $25 because this is how much you have in your pocket.



So the equation is <font size=4 color="red">2b + 7 = 25</font>


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If you want to solve for b, then...



2b + 7 = 25


2b + 7-7 = 25-7


2b + 0 = 18


2b = 18


2b/2 = 18/2


b = 9



Therefore, you can buy 9 books with $25. If you only want the equation, then ignore this portion. However, it is useful to know how solve equations.