You and your friend are selling tickets to a charity event. you sell 8 adult tickets and 6 student tickets for $126. your friend sells 12 adult tickets and 13 student tickets for $209. what is the cost of a student ticket?

S=cost per student ticket
a=cost per adult ticket

value=(students vlue)+(adults value)
student value=(cost per student) times number of students
adult value=(cost per adult) times number of adults

you sell 8 adult and 6 students and that is a value of 126
8a+6s=126

friend sell12 adult and 13 student and get 209
12a+13s=209

so we have
8a+6s=126 and
12a+13s=209
it might help to simplify  the first equaiton by dividing by 2
4a+3s=63

we have
4a+3s=63
12a+13s=209
multiply first equaton by -3
-12a-9s=-189

add to secont equaiton

12a+13s=209
-12a-9s=-189 +
0a+4s=20

4s=20
divide 4
s=5

each student ticket costs $5.00

The answer of the above is