The escalator travels from bottom to top at a uniform speed. The boy takes 120 steps per minute, and the girl takes 80 steps per minute. The boy takes 30 seconds to reach the upper floor, and the girl takes 40 seconds to reach the upper floor. How many steps does the escalator have?
自动扶梯以均匀速度由下向上行驶，男孩每分走120级阶梯，女孩每分走80级阶梯，男孩用30秒到楼上，女孩用40秒到楼上，该扶梯共有几级阶梯？
<gadget id="calculator">120 * 30</gadget>
<output>3_600</output>

<gadget id="calculator">80 * 40</gadget>
<output>3_200</output>

<gadget id="calculator">3_600 - 3_200</gadget>
<output>400</output>

<gadget id="calculator">40 - 30</gadget>
<output>10</output>

<gadget id="calculator">400 / 10</gadget>
<output>40</output>

<gadget id="calculator">30 * 40</gadget>
<output>1_200</output>

<gadget id="calculator">3_600 + 1_200</gadget>
<output>4_800</output>

<result>4_800</result>