so you can do this by using a system of equations
x=student tickets
y=adult tickets
x+y=394
x+56=y
then you substitute y in
x+(x+56)=394
2x+56=394
2x=394-56
2x=338
x=169 which is the number of student tickets
then you find the amount of adult tickets
x+56=y
169+56=y
225=y
and now you can check it
225+169=394
394=394
Answer:
169 student tickets were sold
225 adult tickets were sold