Sebastian's retirement party will cost $324 if he invites 18 guests. If there are 28 guests, how much will Sebastian's retirement party cost? Solve using unit rates.
The cost of Sebastian's retirement party is $324 for 18 guests. To find the cost per guest, we can divide the total cost by the number of guests: $324 / 18 guests = $<<324/18=18>>18/guest.
To find the cost for 28 guests using unit rates, we multiply the cost per guest by the number of guests: $18/guest * 28 guests = $504. Answer: \boxed{504}.