ok so you have to use 2 equations
a- adults s- students
7a+4s=380
a+s=80 and that turns into s=80-a
now use substitution
7a+4(80-a)= 380
7a+320-4a=380
3a=60
ADULT TICKETS- 20
now solve for student tickets
20+s=80
STUDENT TICKETS- 60
so 20 adult tickets and 60 student tickets