The length of the railway between A and B is 420 km. A train of passenger cars and a train of freight trains depart from Station A and Station B at the same time. After how many hours did the two cars meet?
甲乙两站之间的铁路长420千米，一列客车和一列货车分别从甲站和乙站同时相对开出，客车每小时行80千米，货车的速度是客车的(3/4)．经过几小时两车相遇？
<gadget id="calculator">3 / 4</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">80 * (3/4)</gadget>
<output>60</output>

<gadget id="calculator">80 + 60</gadget>
<output>140</output>

<gadget id="calculator">420 / 140</gadget>
<output>3</output>

<result>3</result>