The distance between A and B is 660 kilometers. A train departs from A to B. It travels 252 kilometers in the first 4.2 hours. If the speed of the remaining distance is increased by 20 kilometers, how many hours will it take to reach B?
甲、乙两地相距660千米，一列火车从甲地出发开往乙地，前4.2小时行了252千米，余下的路程如果速度增加20千米，还要几小时才能到达乙地？
<gadget id="calculator">660 - 252</gadget>
<output>408</output>

<gadget id="calculator">252 / 4.2</gadget>
<output>60</output>

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

<gadget id="calculator">408 / 80</gadget>
<output>51/10 = around 5.1</output>

<result>51/10 = around 5.1</result>