Question 139751
What I think you really want is a linear function that models the cost for ANY number of people, and then use that model to calculate the cost for 60 people.


Let x be the number of people.  Each one costs $12, so the cost for the people is 12x.  But there is also the $75 that is charged whether anyone attends or not, so:


{{{C(x)=12x+75}}}, where C is the cost function and x is the number of people who attend.


Now, you want to know the cost for 60 people.  So just evaluate {{{C(60)}}}, which is to say, substitute 60 in place of x in your model and do the arithmetic.