Carla's retirement party will cost $15 if she invites 3 guests. If there are 4 guests, how much will Carla's retirement party cost? Assume the relationship is directly proportional.

If there are 4 guest Carla's retirement party will cost $20.

Step-by-step explanation:

First, you have to figure out how much money is needed for one guest;

15:3 = $5

Each guest costs $5. Now you just multiply by 5 by 4.

Thus, the answer is $20.