long-distance bus and a truck depart from two places 550 kilometers apart at the same time and head toward each other. The passenger car travels 90 kilometers per hour. It takes half an hour to get on and off the bus, and the truck travels 80 kilometers per hour. How many hours does it take for the truck to meet the passenger car?
一辆长途客车和一辆货车同时从相距550千米的两地出发，相向而行．客车每小时行90千米，中途因为上下客停站用了半小时，货车每小时行80千米，货车行驶几小时后与客车相遇？
<gadget id="calculator">80 * 0.5</gadget>
<output>40</output>

<gadget id="calculator">550 - 40</gadget>
<output>510</output>

<gadget id="calculator">90 + 80</gadget>
<output>170</output>

<gadget id="calculator">510 / 170</gadget>
<output>3</output>

<gadget id="calculator">3 + 0.5</gadget>
<output>3.5</output>

<result>3.5</result>