Since we are given the actual costs as well as the final total then we can calculate the total number of people that attended the party by doing the following. We first subtract the fixed cost of $120 by the total cost of the party, and then we divide the remainder by the cost per person, which would give us the number of people who attended (x) ...
($480 - $120) / $15 = x
$360 / $15 = x
24 = x
Finally, we can see that a total number of 24 individuals attended the party
