A cylinder is cut through the center of the bottom surface along the height, and the surface area increases by 30 square centimeters. If the height of the cylinder is 5 centimeters, what is the area of the bottom of the cylinder?
一个圆柱过底面圆心沿高切开，表面积增加了30平方厘米，已知圆柱的高为5厘米，则圆柱的底面积为多少．
<gadget id="calculator">30 / 2 / 5 / 2</gadget>
<output>3/2 = around 1.5</output>

<gadget id="calculator">(3/2) ** 2</gadget>
<output>9/4 = around 2.25</output>

<gadget id="calculator">3.14 * (9/4)</gadget>
<output>7.065</output>

<result>7.065</result>