There are 20 seats in a row of a movie theater. 3 good friends go to the movies together. They choose the 6th row and want to sit together. How many different ways of sitting are there?
电影院一排有20个座位，3个好朋友一起去看电影，他们选择了第6排，并且要坐在一起，请问有多少种不同的坐法．
<gadget id="calculator">20 - 3</gadget>
<output>17</output>

<gadget id="calculator">17 + 1</gadget>
<output>18</output>

<gadget id="calculator">3 + 2 + 1</gadget>
<output>6</output>

<gadget id="calculator">18 * 6</gadget>
<output>108</output>

<result>108</result>