An isosceles trapezoid has an upper base of 4 meters, a height of 30 decimeters, and a base of 12 meters. What is the area of the trapezoid in square meters?
一个等腰梯形，上底是4米，高是30分米，底是12米，这个梯形的面积是多少平方米．
<gadget id="calculator">30 / 10</gadget>
<output>3</output>

<gadget id="calculator">4 + 3</gadget>
<output>7</output>

<gadget id="calculator">12 / 2</gadget>
<output>6</output>

<gadget id="calculator">7 * 6</gadget>
<output>42</output>

<result>42</result>