One side of the jumping box for the sports group is trapezoidal, its upper base is 8 decimeters, its lower base is 1 meter, and its height is 11 decimeters. What is the area of this trapezoid in square decimeters?
体育组跳箱的一面是梯形，它的上底是8分米，下底是1米，高11分米．求这个梯形的面积是多少平方分米？
<gadget id="calculator">1 * 10</gadget>
<output>10</output>

<gadget id="calculator">8 + 10</gadget>
<output>18</output>

<gadget id="calculator">11 / 2</gadget>
<output>11/2 = around 5.5</output>

<gadget id="calculator">18 * (11/2)</gadget>
<output>99</output>

<result>99</result>