If a cylindrical piece of wood is cut into 3 sections, the surface area increases by 28 square centimeters, what is the cross-sectional area of this piece of wood in square centimeters?
把一根圆柱形木料截成3段，表面积增加了28平方厘米，这根木料的横截面积是多少平方厘米．
<gadget id="calculator">28 / 4</gadget>
<output>7</output>

<result>7</result>