passenger car and a freight car leave from two places A and B which are 490 kilometers apart at the same time. It is known that the passenger car travels 60 kilometers per hour. After 4 hours, the distance between the two cars is still 50 kilometers. How many kilometers does the truck travel per hour?
客车和货车分别从相距490千米的甲乙两地同时相向开出，已知客车每小时行60千米，4小时后，两车还相距50千米．求货车每小时行多少千米？
<gadget id="calculator">490 - 50</gadget>
<output>440</output>

<gadget id="calculator">440 / 4</gadget>
<output>110</output>

<gadget id="calculator">110 - 60</gadget>
<output>50</output>

<result>50</result>