Xiao Ming and Xiao Hong walk in the opposite direction of the escalator. In 10 seconds, Xiao Ming walks 15 steps, and Xiao Hong walks 13 steps. As a result, when reaching the other end, Xiao Ming walked for 1 minute, and Xiao Hong walked for 1.5 minutes. How many steps are there in the visible part of the escalator at rest?
小明和小红逆着自动扶梯行驶方向行走，10秒里小明走15级，小红走13级．结果到达另一端时，小明走了1分钟，小红走了1.5分钟．扶梯静止时可见部分共有多少级．
<gadget id="calculator">60 / 10</gadget>
<output>6</output>

<gadget id="calculator">6 * 15</gadget>
<output>90</output>

<gadget id="calculator">90 / 10</gadget>
<output>9</output>

<gadget id="calculator">9 * 13</gadget>
<output>117</output>

<gadget id="calculator">117 - 90</gadget>
<output>27</output>

<gadget id="calculator">1.5 - 1</gadget>
<output>0.5</output>

<gadget id="calculator">27 / 0.5</gadget>
<output>54</output>

<gadget id="calculator">54 * 1</gadget>
<output>54</output>

<gadget id="calculator">90 - 54</gadget>
<output>36</output>

<result>36</result>