Some students stand in a row with an interval of 2 meters. There are 4 people in front of Wang Qiang and 5 people behind him. How long is this line?
有一些同学站成一行，间隔2米．王强前面有4人，后面有5人，这条队伍长多少．
<gadget id="calculator">1 - 1</gadget>
<output>0</output>

<gadget id="calculator">5 + 4 + 0</gadget>
<output>9</output>

<gadget id="calculator">9 * 2</gadget>
<output>18</output>

<result>18</result>