The answer is 112 im pretty sure!
The two equations are

and

the first equation can be solved for x to be

next you can substitute x in the second equation

Distribute 4 to everything in the parentheses

combine like terms:

subtract 28 from both sides of the equation

divide both sides by -1.5

plug this in to the original equation of x+y=7

subtract 4 from both sides.

Final Answer: they bought 3 adult tickets and 4 student tickets
Hope this helps!
53: 800 and 900
54: 700 and 800
55: 500 and 600
56: 2,771,100 and 2,771,200
57: 90,120,000 and 90,120,100
58: 631,900 and 632,000
59: 93,300 and 93,400
60: 200 and 300
61: 900 and 1000
62: 39,576,700 and 39,576,800
63: 24,900 and 25,000
64: 471,100 and 471,200