An express train and a slow train leave opposite directions at the same time from two places 480 kilometers apart, and meet each other 4 hours later. It is known that the speed of the express train is 70 kilometers per hour, how many kilometers per hour does the slow train travel?
一列快车和一列慢车同时从相距480千米的两地相向开出，4小时后相遇．已知快车的速度是每小时行70千米，慢车每小时行多少千米？
<gadget id="calculator">480 / 4</gadget>
<output>120</output>

<gadget id="calculator">120 - 70</gadget>
<output>50</output>

<result>50</result>