Question 1129988
sum=(n/2)(2a+(n-1)d)=13(16+(25)(2))=13*66=858 seats

student=x
adult=858-x
x=2(858-x)
3x=1716
x=572 student tickets and 286 adult tickets
student ticket costs y
adult ticket costs 3y
572y+286(3y)=2860
1430y=2860
y=$2, student ticket cost
3y=$6, adult ticket cost