On a map with a scale of 1:4,000,000, the distance between A and B is 9cm. Cars A and B set off from A and B at the same time, drive toward each other, and meet each other in 3 hours. The speed ratio of cars A and B is 5:7, find the speed of car B.
在一幅比例尺是1：4000000的地图上，量得A、B两地的距离是9cm，甲、乙两车分别从A、B两地同时出发，相向而行，3小时相遇．甲、乙两车的速度比是5：7，求乙车的速度．
<gadget id="calculator">1 / 4_000_000</gadget>
<output>1/4_000_000 = around 0</output>

<gadget id="calculator">9 / (1/4_000_000) / 100_000 / 3</gadget>
<output>120</output>

<gadget id="calculator">5 + 7</gadget>
<output>12</output>

<gadget id="calculator">7 / 12</gadget>
<output>7/12 = around 0.583333</output>

<gadget id="calculator">120 * (7/12)</gadget>
<output>70</output>

<result>70</result>