The distance between A and B cities is 780 kilometers. A bus and a truck leave from the two places respectively. The bus travels 100 kilometers per hour, and the truck travels 80 kilometers per hour. The truck leaves only 1.5 hours after the departure of the passenger car. How long does it take for the truck to run from departure to when the two vehicles meet?
甲乙两城相距780千米，一辆客车和一辆货车分别从两地相对开出，客车每时行100千米，货车每时行80千米．客车出发1.5时后货车才出发，货车从出发到两车相遇行了几时？
<gadget id="calculator">100 * 1.5</gadget>
<output>150</output>

<gadget id="calculator">780 - 150</gadget>
<output>630</output>

<gadget id="calculator">100 + 80</gadget>
<output>180</output>

<gadget id="calculator">630 / 180</gadget>
<output>7/2 = around 3.5</output>

<result>7/2 = around 3.5</result>