https://www.gregmat.com/quizzes/quiz/im-overwhelmed-algebra-progress-quiz-6-version-2 (Question 18)
The question says that one more person arrives on the 8th day so technically on the eight day that person will be consuming food as well. In the solution we calculated the food consumed for 6 people for 3 days interval (6th 7th and 8th) when I assume it should be 2 days