A People's Liberation Army team is 450 meters long and travels at a speed of 1.5 meters per second. How long does it take for a fighter to travel from the rear of the platoon to the head of the platoon at a speed of 3 meters per second and immediately return to the rear of the platoon?
某解放军队伍长450米，以每秒1.5米的速度行进．一战士以每秒3米的速度从排尾到排头并立即返回排尾，那么这需要多少时间？
<gadget id="calculator">3 - 1.5</gadget>
<output>1.5</output>

<gadget id="calculator">450 / 1.5</gadget>
<output>300</output>

<gadget id="calculator">3 + 1.5</gadget>
<output>4.5</output>

<gadget id="calculator">450 / 4.5</gadget>
<output>100</output>

<gadget id="calculator">300 + 100</gadget>
<output>400</output>

<result>400</result>