Dolly wants to ride the Ferris wheel twice, the roller coaster three times, and the log ride seven times. The Ferris wheel costs 2 tickets, the roller coaster costs 5 tickets and the log ride costs 1 ticket. Dolly has 20 tickets. How many more tickets should Dolly buy? Think carefully first, then make a decision:

Show your work and conclude with the exact phrasing "Therefore, the final answer is [answer]." where [answer] is just the final number or expression that solves the problem.
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It costs 2 rides x 2 tickets / ride = 4 tickets to ride the Ferris wheel twice. It costs 3 rides x 5 tickets / ride = 15 tickets to ride the roller coaster three times. It costs 7 rides x 1 ticket / ride = 7 tickets to ride the roller coaster seven times. In total Dolly needs 4 tickets + 15 tickets + 7 tickets = 26 tickets. Dolly needs to buy 26 tickets - 20 tickets = 6 more tickets. So, the answer is 6.