In a certain battle, according to the report of our scouts, the enemy army was fleeing south at a speed of 5.5 kilometers per hour in a place 6 kilometers south of me. Our army immediately pursued the enemy at a speed of 8.5 kilometers per hour. After catching up with the enemy, it took only half an hour to wipe out the enemy army. Question: How long did it take from the beginning of the pursuit to the complete annihilation of the enemy army?
某次战役中，根据我侦查员报告，敌军在我南面6千米的某地正以每小时5.5千米的速度向南逃窜，我军立即以每小时8.5千米的速度追击敌人，在追上敌人后只用半小时就全歼灭敌军．问：从开始追击到全歼灭敌军，共用了多长时间？
<gadget id="calculator">8.5 - 5.5</gadget>
<output>3</output>

<gadget id="calculator">6 / 3</gadget>
<output>2</output>

<gadget id="calculator">2 + 0.5</gadget>
<output>2.5</output>

<result>2.5</result>