An isosceles triangle vegetable field has a circumference of 160 meters and a waist length of 50 meters. The height on the bottom edge is 30 meters, what is the area of this vegetable field in square meters?
一块等腰三角形菜地周长160米，腰长50米．底边上的高30米，这块菜地的面积是多少平方米？
<gadget id="calculator">160 - 50 - 50</gadget>
<output>60</output>

<gadget id="calculator">30 / 2</gadget>
<output>15</output>

<gadget id="calculator">60 * 15</gadget>
<output>900</output>

<result>900</result>