The school arranges a labor task. If Class A is assigned to do it alone, it will take a hour to complete it; if Class B is assigned to do it alone, it will take b hours to complete it. In order to complete the task as soon as possible, the school assigns Class A and Class B to complete the task together. Ask this How many hours will it take for the two classes to work together to complete the task? If it takes 6 hours for Class A to complete the task alone, and 12 hours for Class B to complete the task alone, how many hours will it take for the two classes to complete the task together?
学校安排一项劳动任务，若单独派甲班所去做，需要a小时完成；单独派乙班去做，需要b小时完成，学校为了尽快完成任务，派甲班和乙班一起完成，问这两个班合作需多少小时完成任务？若甲班单独完成需6小时，乙班单独完成需12小时，则两班合作需几小时完成任务？
<gadget id="calculator">1 / 6</gadget>
<output>1/6 = around 0.166667</output>

<gadget id="calculator">1 / 12</gadget>
<output>1/12 = around 0.083333</output>

<gadget id="calculator">(1/6) + (1/12)</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1 / (1/4)</gadget>
<output>4</output>

<result>4</result>