For a parallelogram, the base remains the same, the height increases by 4 cm, and the area increases by 36 cm2; the height remains the same, the base increases by 5 cm, and the area increases by 20 cm2, find the area of the original parallelogram.
一个平行四边形，底不变，高增加4厘米，面积增加36平方厘米；高不变，底增加5厘米，面积增加20平方厘米，求原来平行四边形的面积．
<gadget id="calculator">20 / 5</gadget>
<output>4</output>

<gadget id="calculator">36 / 4</gadget>
<output>9</output>

<gadget id="calculator">4 * 9</gadget>
<output>36</output>

<result>36</result>