The distance between places A and B is 420 meters. Cars A and B drive towards each other at the same time. They meet after 3 hours. It is known that the speed ratio of cars A and B is 3:4. How many kilometers does car B travel per hour?
A、B两地相距420米，甲乙两辆汽车同时从两地相向开出，3小时后相遇，已知甲、乙两车的速度比是3：4，乙车每小时行多少千米？
<gadget id="calculator">420 / 3</gadget>
<output>140</output>

<gadget id="calculator">3 + 4</gadget>
<output>7</output>

<gadget id="calculator">4 / 7</gadget>
<output>4/7 = around 0.571429</output>

<gadget id="calculator">140 * (4/7)</gadget>
<output>80</output>

<result>80</result>