There are 7 stations on the East Ring Railway from Haikou to Sanya, and one kind of ticket is designed for every two stations. How many kinds of tickets should be designed in total?
东环铁路海口至三亚一共有7个站点，每两个站点设计一种车票，一共要设计多少种车票．
<gadget id="calculator">6 + 5 + 4 + 3 + 2 + 1</gadget>
<output>21</output>

<gadget id="calculator">21 * 2</gadget>
<output>42</output>

<result>42</result>