A group of university students are polled on their food preferences. Of the group, 35 liked pies, 54 liked pizza and 65 liked burgers. Fifteen of the students liked pies and burgers, 23 liked burgers and pizza, and 22 liked pies and pizza. There were 15 students who liked all three foods. If 110 students were polled, how many must have answered that they did not like any of the foods? please help me, thank you .