Along the escalator that rises at a constant speed, A walks 150 steps from top to bottom, and B walks 75 steps from bottom to top. If the number of escalator steps that A walks per minute is 3 times that of B, how many steps (visible parts) does this escalator have?
沿着匀速成上升的自动扶梯，甲从上朝下走到底走了150级，乙从下朝上走到顶走了75级．如果甲每分钟走的扶梯级数是乙的3倍，那么这部自动扶梯有多少级(可见部分)？
<gadget id="calculator">150 * 3</gadget>
<output>450</output>

<gadget id="calculator">75 * 2</gadget>
<output>150</output>

<gadget id="calculator">450 + 150</gadget>
<output>600</output>

<gadget id="calculator">3 + 2</gadget>
<output>5</output>

<gadget id="calculator">600 / 5</gadget>
<output>120</output>

<result>120</result>