Answer:
There were 5 adults tickets and 3 Children tickets bought
Explanation:
1 ticket; 33$ for an Adult
1 ticket; 21$ for children 
There are 8 people who bought tickets
Let's set Adult as a
Let's set Children as c
Let's find A first
a + c = 8 
a = 8 - c 
Now, (8-c) stands for A/adults
33(8-c) + 21(c) = 228
33(8) + 33(-c) + 21c = 228
264-33c + 21c = 228
-33c+21c = 228-264
-12c = -36 
c = -36/-12 
c = 3 
So there were 3 children, 
Let's apply this rule again, 
a + 3 = 8 
a = 8 - 3 
a = 5 
So that means that there were 5 Adults and 3 Children,