A travels 12 kilometers per hour, B travels 9 kilometers per hour, and they both go from the east city to the west city at the same time. After A travels 15 kilometers, he goes back to pick up his stuff, and immediately chases after B after picking up his stuff. (The time taken to pick up the stuff is ignored). When he catches up with B, he just arrives at the west city. How many thousands are the distance between the east and west cities? rice?
甲每小时行12千米，乙每小时行9千米，二人同时由东城去西城．甲行15千米后，又回去去取东西，取完东西立即向乙追去，(取东西的时间忽略不计)当他追上乙时恰好已到西城，求东、西两城相距多少千米？
<gadget id="calculator">12 - 9</gadget>
<output>3</output>

<gadget id="calculator">2 / 3</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">15 * (2/3)</gadget>
<output>10</output>

<gadget id="calculator">9 * 10</gadget>
<output>90</output>

<result>90</result>