Ahmed Issah

i tried working this and am getting negative answers and i doubt my answers because it not possible to get negative number of people. PLEASE HELP ME QUESTION A college doctor found out that 40 students have had food poisoning. He found out the following after interviewing them. 25, 27 and 30 took rice, beans and plantain respectively. 28 took rice or plantain but not beans 13 took rice and plantain 10 took rice but did not take beans and plantain 7 took beans and plantain but not rice determine the number of students who a. took none of the meal b. took all the three meal c. took only one meal d. took more than one meal