Given that for every 3 tickets, Jenny charges $18.
Let's find the amount charged for 1 ticket:
Therefore, Jenny charges $6 for each ticket.
For 5 tickets, the charge is:
5 * 6 = $30
For 7 tickets, the charge is:
7 * 6 = $42
For 10 tickets, the charge is:
10 * 6 = $60
For 8 tickets, the charge is:
8 * 6 = $48