Hi
let's call X : adults entries and Y = students entries
so : 5X+Y = 2 679 and X+Y = 1 127 so Y = 1127 -X
so : 5X +1127-X = 2 679
4X = 2679 -1127
4X = 1552
X = 1552 /4 = 388
so there is 388 adults tickets sold
So as X = 388
we have : 388 +Y = 1127
Y = 1127 -388 = 739
let's check : 5 * 388 + 739 =2679
388 + 739 = 1 127