Let the number of adult be x and the number of children be y.
There is a total of 11 people
x + y = 11
Total cost of tickets is $228
22x + 15y = 228
x + y = 11 ----------------- (1)
22x + 15y = 228 ---------(2)
From (1):
x+ y = 11
x = 11 - y --- sub into (2)
22 (11 - y) + 15y = 228
242 - 22y + 15y = 228
-7y = 228 - 242
-7y = -14
y = 2 ---- sub into (1)
x+ 2 = 11
x = 9
Number of adult tickets = 9
Number of child tickets = 2