If a passenger car traveling 50 kilometers per hour chases a truck traveling 90 kilometers first, and catches up after traveling 450 kilometers, how many kilometers per hour does the truck travel?
一辆每小时行50千米的客车去追一辆先行90千米的货车，已知行了450千米后追上，那么货车每小时行多少千米？
<gadget id="calculator">450 - 90</gadget>
<output>360</output>

<gadget id="calculator">450 / 50</gadget>
<output>9</output>

<gadget id="calculator">360 / 9</gadget>
<output>40</output>

<result>40</result>