The distance between A and B is 391.5 kilometers. A passenger car travels from A to B at 52 kilometers per hour. After driving for 1 hour, a truck travels from B to A at 45 kilometers per hour. M, how long did the two cars meet after the truck drove out?
甲、乙两地相距391.5千米，一辆客车从甲地开往乙地，每小时行52千米，行了1小时后，一辆货车从乙地开往甲地，每小时行45千米，货车开出几时后两车相遇？
<gadget id="calculator">391.5 - 52</gadget>
<output>339.5</output>

<gadget id="calculator">52 + 45</gadget>
<output>97</output>

<gadget id="calculator">339.5 / 97</gadget>
<output>3.5</output>

<result>3.5</result>