semi-circular reservoir, A starts from the management office beside the reservoir, and patrols along the embankment at a speed of 2.5 kilometers per hour. Three hours later, B also set off from the management office, patrolling along the embankment at a speed of 4 kilometers per hour, and they returned to the starting point at the same time. If π takes an approximate value of 3, what is the area of the reservoir in square kilometers?
一个半圆形的水库，甲从水库边的管理处出发，以每小时2.5千米的速度沿堤岸绕行巡逻．三小时后乙也从管理处出发，以每小时4千米的速度沿堤岸绕行巡逻，他们同时回到出发点．如果π取近似值3，那么水库的面积是多少平方千米．
<gadget id="calculator">4 ** 2</gadget>
<output>16</output>

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

<gadget id="calculator">3 * 16 * (1/2)</gadget>
<output>24</output>

<result>24</result>