The distance between A and B is 240 kilometers. A truck full of goods transports goods from A to B. It arrives in 6 hours. When it returns, it travels an extra 20 kilometers per hour because it is empty. How long does it take for this truck to return to A? land?
甲乙两地相距240千米，一辆货车满载货物从甲地运往乙地，去时6小时到达，返回时，由于空载，每小时多行20千米，问这辆货车几小时可以返回甲地？
<gadget id="calculator">240 / 6</gadget>
<output>40</output>

<gadget id="calculator">40 + 20</gadget>
<output>60</output>

<gadget id="calculator">240 / 60</gadget>
<output>4</output>

<result>4</result>