For a rectangle, if the length is increased by 9 meters or the width is increased by 5 meters, the area can be increased by 450 square meters. Find the area of the original rectangle.
一个长方形，如果长增加9米或者宽增加5米，面积都可以增加450平方米．求原来长方形的面积．
<gadget id="calculator">450 / 9</gadget>
<output>50</output>

<gadget id="calculator">450 / 5</gadget>
<output>90</output>

<gadget id="calculator">50 * 90</gadget>
<output>4_500</output>

<result>4_500</result>