The express train and the slow train leave opposite each other from two cities 630 kilometers apart at the same time. The express train travels 70 kilometers per hour, and the speed of the slow train is 80% of the speed of the express train. How many hours later do the two cars meet?
快车和慢车同时从相距630千米的两城市相对开出，快车每小时行70千米，慢车的速度是快车的80%，开出几小时后两车相遇？
<gadget id="calculator">80 / 100</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">70 * (4/5)</gadget>
<output>56</output>

<gadget id="calculator">70 + 56</gadget>
<output>126</output>

<gadget id="calculator">630 / 126</gadget>
<output>5</output>

<result>5</result>