15 people, each want 2 hamburgers, so there will be 15*2 = 30 hamburgers.
However, we only want the plain hamburgers.
3 people want hamburgers with cheese: 30-3 = 27 plain hamburgers
2 people want hamburgers with mustard: 27-2 = 25 plain hamburgers
2 people want hamburgers with catsup: 25-2 = 23 plain hamburgers
Jim and his dad will make 23 plain hamburgers.
Hope this helps!! Let me know if you have ANY questions.