The upper base of the trapezoid is 12 decimeters, the lower base is 1 decimeter more than three times the upper base, and the height is 5 decimeters. What is the area of the trapezoid in square decimeters?
梯形的上底是12分米，下底比上底的3倍还多1分米，高是5分米，这个梯形的面积是多少平方分米．
<gadget id="calculator">12 * 3</gadget>
<output>36</output>

<gadget id="calculator">36 + 1</gadget>
<output>37</output>

<gadget id="calculator">12 + 37</gadget>
<output>49</output>

<gadget id="calculator">5 / 2</gadget>
<output>5/2 = around 2.5</output>

<gadget id="calculator">49 * (5/2)</gadget>
<output>245/2 = around 122.5</output>

<result>245/2 = around 122.5</result>