postman needs to send a letter to a certain place by bicycle within the specified time. If he walks 15 kilometers per hour, he can arrive 0.4 hours early, and if he walks 12 kilometers per hour, he will arrive 0.25 hours late. How far? (solution by equation)
一个邮递员需要在规定时间内骑自行车把信件送到某地，如果每小时走15千米，可早到0.4小时，如果每小时走12千米，则迟到0.25小时，他去某地的路程有多远？(用方程解)
<gadget id="calculator">0.4 + 0.25</gadget>
<output>0.65</output>

<gadget id="calculator">1 / 12</gadget>
<output>1/12 = around 0.083333</output>

<gadget id="calculator">1 / 15</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">(1/12) - (1/15)</gadget>
<output>1/60 = around 0.016667</output>

<gadget id="calculator">0.65 / (1/60)</gadget>
<output>39</output>

<result>39</result>