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?
It costs 2 rides x 2 tickets/ride = 
<gadget id="calculator">2*2</gadget>
<output>4</output>
4 tickets to ride the Ferris wheel twice.
It costs 3 rides x 5 tickets/ride = 
<gadget id="calculator">3*5</gadget>
<output>15</output>
15 tickets to ride the roller coaster three times.
It costs 7 rides x 1 ticket/ride = 
<gadget id="calculator">7*1</gadget>
<output>7</output>
7 tickets to ride the roller coaster seven times.
In total Dolly needs 4 tickets + 15 tickets + 7 tickets = 
<gadget id="calculator">4+15+7</gadget>
<output>26</output>
26 tickets.
Dolly needs to buy 26 tickets - 20 tickets = 
<gadget id="calculator">26-20</gadget>
<output>6</output>
6 more tickets.

<result>6</result>