Dish problem

 Every people needs to use 1/2 dish rice, 1/3 dish broth, and 1/4 dish meat. So,  the minimal possible number is 13/12 dishes for each, and the number of all customer must be the multiple of 12 (LCM of 2, 3 and 4). So we got 65/ (13/12)= 60, and 60 is also a multiple of 12.
Check the answer, 60 customers, need 30 dishes rice, 20 dishes broth, and 15 dishes of meat. Therefore, the final answer is the max of the 60 customers.