The upper base of a trapezoid is 12 decimeters, the lower base is 48 decimeters, and the height is half of the sum of the upper and lower bases. What is the area of the trapezoid in square decimeters?
一个梯形的上底是12分米，下底是48分米，高等于上、下底和的一半，那么梯形的面积是多少平方分米．
<gadget id="calculator">12 + 48</gadget>
<output>60</output>

<gadget id="calculator">60 / 2</gadget>
<output>30</output>

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

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

<result>900</result>