A piece of rectangular cardboard, after subtracting 5 cm from the long side and 2 cm from the wide side, we get a square whose area is 31 square centimeters less than the original rectangle. Find the area of the original rectangle.
一块长方形纸板，长边减去5厘米，宽边减去2厘米后，得到一个正方形，面积比原长方形少31平方厘米．求原长方形的面积．
<gadget id="calculator">3 + 5</gadget>
<output>8</output>

<gadget id="calculator">3 + 2</gadget>
<output>5</output>

<gadget id="calculator">8 * 5</gadget>
<output>40</output>

<result>40</result>