Cars A and B leave opposite directions from cities A and B at the same time, and meet at the 21 km midway point after a certain amount of time. It is known that the speed of car A is 1.5 times that of car B, and how many kilometers are the distance between the two cities.
甲乙两车同时从A、B两城相向开出，若干时间后在过路程中点21千米处相遇．已知甲车行驶的速度是乙车的1.5倍，甲乙两城相距多少千米．
<gadget id="calculator">21 * 2</gadget>
<output>42</output>

<gadget id="calculator">3 - 2</gadget>
<output>1</output>

<gadget id="calculator">42 / 1</gadget>
<output>42</output>

<gadget id="calculator">3 + 2</gadget>
<output>5</output>

<gadget id="calculator">42 * 5</gadget>
<output>210</output>

<result>210</result>