The distance between A and B is 420 kilometers. One section of the road is an asphalt road, and the other section is a dirt road. A car travels from A to B in 8 hours. It is known that its speed is 60 kilometers per hour on the asphalt road and 40 kilometers per hour on the dirt road. How many miles is the dirt road?
甲、乙两地相距420千米，其中一段路面是柏油路，另一段是土路．一辆汽车用8小时从甲地驶达乙地，已知它在柏油路上行驶的速度是每小时60千米，而在土路上的行驶速度是每小时40千米．土路长多少千米？
<gadget id="calculator">60 * 8</gadget>
<output>480</output>

<gadget id="calculator">480 - 420</gadget>
<output>60</output>

<gadget id="calculator">60 - 40</gadget>
<output>20</output>

<gadget id="calculator">60 / 20</gadget>
<output>3</output>

<gadget id="calculator">40 * 3</gadget>
<output>120</output>

<result>120</result>