Karen invited 150 friends to her 15th birthday party, but not everyone can attend,  Karen’s mother want one adult for every 25 of her friends.  The cost of food is $20 for every four of her friends, and the adults eat  for free.  If a total of 116 people (including Karen and her mother) go to the party, how many are adults and how many are Karen’s friends? How much will the food cost? Explain how you found your answer.