The height of a cylinder is reduced by 2cm, and its surface area is reduced by 31.4cm**2 from the original. What is the area of the bottom of the cylinder in cm**2?
一个圆柱的高减少2cm，它的表面积比原来减少了31.4cm**2，这个圆柱的底面积是多少cm**2．
<gadget id="calculator">31.4 / 2</gadget>
<output>15.7</output>

<gadget id="calculator">15.7 / 3.14 / 2</gadget>
<output>2.5</output>

<gadget id="calculator">2.5 ** 2</gadget>
<output>6.25</output>

<gadget id="calculator">3.14 * 6.25</gadget>
<output>19.625</output>

<result>19.625</result>