An escalator moves upwards at a constant speed. Two people, A and B, reach the upper floor from the bottom of the escalator at the same time. The speed of A is twice that of B. When A walked 27 levels to reach the upstairs, B walked 18 levels. How many steps are there in the exposed part of the escalator?
自动扶梯匀速向上行使，甲乙两人同时从扶梯底部到达楼上，甲速度是乙的2倍．当甲走了27级到达楼上时，乙走了18级．问扶梯露在外面部分有多少级？
<gadget id="calculator">27 - 18</gadget>
<output>9</output>

<gadget id="calculator">27 / 2</gadget>
<output>27/2 = around 13.5</output>

<gadget id="calculator">18 - (27/2)</gadget>
<output>9/2 = around 4.5</output>

<gadget id="calculator">9 / (9/2)</gadget>
<output>2</output>

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

<gadget id="calculator">3 * 18</gadget>
<output>54</output>

<result>54</result>