Answer:
75 students are going. 15 adults are going.
Step-by-step explanation:
Since the question says there are 90 tickets in total, 75 student ticket plus 15 adult tickets equals 90 tickets in total. Also 75 divided by 15 is 5, which suits the ratio of 5 students to per adult.
There wasn't enough information for me to solve the last one, but I hope this helps!