A certain unit organized employees to go on a spring outing. After the train traveled at a speed of 138 kilometers per hour for 15 hours, it was still 6 kilometers away from the destination. If the return journey must be made within 12 hours, what is the minimum speed of the train on the return journey?
某单位组织员工去春游，火车以每小时138千米的速度行驶了15小时后，距目的地还有6千米．如果返程必须在12小时以内返回，那么返程时火车的速度最少是多少？
<gadget id="calculator">138 * 15</gadget>
<output>2_070</output>

<gadget id="calculator">2_070 + 6</gadget>
<output>2_076</output>

<gadget id="calculator">2_076 / 12</gadget>
<output>173</output>

<result>173</result>