From the statement of the equation we can express the money spent by each student (s) with this equation:
s=x+20
where x is the cost of the ticket and 20 is the cost of the t-shirt.
Since we know that there are 10 students in total, we can get the total money spent by the students (ts) by multiplying the equation s=x+20 by 10, like this:
ts=(x+20)*10=10x+200
We know that each ticket cost 5 times more for an adult than for a student, then we can express the equation that models the money spent by each adult (a) like this:
a=5x+25
Where 5x is the cost of the ticket and 25 is the cost of the shirt.
Since there are 4 adults, by multiplying this equation by 4, we can get the total money spent by the group of adults (ta), like this:
ta=(5x+25)*4=20x+100
We are told that the group of students spent the same that the group of adults in total, then we can make the expressions that model the money spent for each group equal like this:
ts=ta
ts=10x+200
ta=20x+100, then:
10x+200=20x+100
By solving for x from this equation we get:
10x+200=20x+100
10x-10x+200-100=20x-10x+100-100
0+100=10x+0
100=10x
10x=100
10x/10=100/10
x=10
Then, the cost of each student ticket is $10