Answer: The answer is 10 students.
Step-by-step explanation: Well first you know 15 take both so you can just subtract 15 from one of the numbers because the same student does not need to be counted twice. I chose to do 35-15 which equals 20. Then you do 60+20 to get 80. Lastly you subtract 80 from 90 to get 10.
I'm gonna go ahead and say I may not be correct because I don't know everything, but I answered to my best ability and got 10.
