Uncle Li drove from Tongren at 7:00 and arrived in Guiyang at 12:00 with a speed of 80km/h. It took 4 hours to return. Was the speed faster or slower when returning? How much is the difference per hour?
李叔叔7：00开车从铜仁出发，12：00到达贵阳，车速为80km/小时，返回时用了4小时，返回时的速度比去时快还是慢？每小时相差多少？
<gadget id="calculator">80 / 4</gadget>
<output>20</output>

<gadget id="calculator">5 * 20</gadget>
<output>100</output>

<gadget id="calculator">100 - 80</gadget>
<output>20</output>

<result>20</result>