vegetable greenhouse covered with plastic film is 15 meters long and its cross-section is a semicircle with a radius of 2 meters. How big is the space in the greenhouse?
一个用塑料薄膜覆盖的蔬菜大棚，长15米，横截面是一个半径2米的半圆．大棚内的空间大约有多大？
<gadget id="calculator">2 ** 2</gadget>
<output>4</output>

<gadget id="calculator">15 / 2</gadget>
<output>15/2 = around 7.5</output>

<gadget id="calculator">3.14 * 4 * (15/2)</gadget>
<output>94.2</output>

<result>94.2</result>