5.50x + 8.70y = 1206.90
x + y = 163.
These are the equations. Now, multiply the second equation by -5.5 so that you can use elimination. You should have -5.50x - 5.50y = 896.5.
Now you have 3.2y = 310.4. Divide and you get 97 adult tickets. Now plug it in to the first equation, so x + 97 = 163, and therefore x = 66 child tickets