x --> represents the students
Then,
each student had two friends come sit with them, tripling the amount: 3x
Then, the entire group divided into five groups: 3x/5
And 4/5 of the students went outside: 3x/5-4/5
Three more people came into the lunch room: 3x/5-4x/5+3
The total number of people in the lunchroom at the end was 11, so: