A train of passenger cars and a train of freight trains leave oppositely from two places at the same time, and the distance between the two cars is 20 kilometers in 4.5 hours. It is known that the speed of the passenger car is 60 kilometers per hour, and the speed of the truck is 70% of the speed of the passenger car. How many kilometers are the distance between the two cities?
一列客车和一列货车同时从两地相对开出，4.5小时两车相距20千米．已知客车的速度是每小时60千米，货车的速度是客车的70%，两城市相距多少千米？
<gadget id="calculator">70 / 100</gadget>
<output>7/10 = around 0.7</output>

<gadget id="calculator">60 * (7/10)</gadget>
<output>42</output>

<gadget id="calculator">60 + 42</gadget>
<output>102</output>

<gadget id="calculator">102 * 4.5</gadget>
<output>459</output>

<gadget id="calculator">459 - 20</gadget>
<output>439</output>

<result>439</result>