The distance between A and B is 380 kilometers. A passenger car drives from A to B at 42 kilometers per hour. After driving 100 kilometers, a truck drives from B to A. After the truck leaves for 3.5 hours The two cars meet. Find the speed of the truck.
甲乙两地相距380千米，一辆客车从甲地开往乙地，每小时行42千米，行了100千米后，一辆货车从乙地开往甲地，货车开出3.5小时后两车相遇．求货车的速度．
<gadget id="calculator">380 - 100</gadget>
<output>280</output>

<gadget id="calculator">280 / 3.5</gadget>
<output>80</output>

<gadget id="calculator">80 - 42</gadget>
<output>38</output>

<result>38</result>