A piece of three-shaped land, the bottom is 28 meters, and the height is the bottom (5/7). What is the area of the land in square meters?
一块三形地，底28米，高是底的(5/7)．这块地的面积是多少平方米？
<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">5 / 7</gadget>
<output>5/7 = around 0.714286</output>

<gadget id="calculator">28 * (5/7)</gadget>
<output>20</output>

<gadget id="calculator">(1/2) * 28 * 20</gadget>
<output>280</output>

<result>280</result>