The highway from Shijiazhuang to Chengde is 546 kilometers long. The Honghong family drove from Shijiazhuang to Chengde to visit the Summer Resort. If they drove an average of 78 kilometers per hour and arrived at 3 pm, when did they leave in the morning?
石家庄到承德的公路长是546千米．红红一家从石家庄开车到承德游览避暑山庄，如果平均每小时行驶78千米，下午3时到达，他们是上午几时出发的？
<gadget id="calculator">546 / 78</gadget>
<output>7</output>

<gadget id="calculator">15 - 7</gadget>
<output>8</output>

<result>8</result>