special force received an anti-terrorism mission in a jungle area, and increased the advancing speed from 60 km/h to 72 km/h. As a result, it arrived at the scheduled location 4 hours ahead of schedule and 36 kilometers away to join the battle. How many hours were spent in the operation.
某特种部队在丛林地区接到一项反恐任务，把推进速度从60千米/小时提高到72千米/小时，结果提前4小时还差36千米就赶到预定地点投人战斗．行动中用了多少小时．
<gadget id="calculator">72 * 4</gadget>
<output>288</output>

<gadget id="calculator">288 - 36</gadget>
<output>252</output>

<gadget id="calculator">72 - 60</gadget>
<output>12</output>

<gadget id="calculator">252 / 12</gadget>
<output>21</output>

<gadget id="calculator">21 - 4</gadget>
<output>17</output>

<gadget id="calculator">36 / 72</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">17 + (1/2)</gadget>
<output>35/2 = around 17.5</output>

<result>35/2 = around 17.5</result>