A car departs from A at 10:00 in the morning and drives to B at a constant speed. It is 390 kilometers away from B at 12:30 noon and 270 kilometers away from B at 2:30 pm. How many kilometers are there between A and B?
一辆汽车上午10：00从甲地出发，开往乙地，一直匀速前进，至中午12：30时距乙地390千米，至下午2：30时距乙地270千米．甲、乙两地相距多少千米？
<gadget id="calculator">390 - 270</gadget>
<output>120</output>

<gadget id="calculator">120 / 2</gadget>
<output>60</output>

<gadget id="calculator">60 * 4.5</gadget>
<output>270</output>

<gadget id="calculator">270 + 270</gadget>
<output>540</output>

<result>540</result>