A and B drove back to back from the same place. After half an hour, A suddenly remembered that he had something to tell B, so he immediately turned around and chased after B. If A travels 80 kilometers per hour and B travels 60 kilometers per hour, how many hours will it take for A to catch up with B?
甲乙两人从同一地点驾车背向而行，经过半小时甲突然想起有事要跟乙说，于是立即调头去追乙．如果甲每小时行80千米，乙每小时行60千米，那么甲追上乙还需要几小时？
<gadget id="calculator">80 + 60</gadget>
<output>140</output>

<gadget id="calculator">80 - 60</gadget>
<output>20</output>

<gadget id="calculator">0.5 / 20</gadget>
<output>0.025</output>

<gadget id="calculator">140 * 0.025</gadget>
<output>3.5</output>

<result>3.5</result>