The perimeter of a square is 120 decimeters, find the area of the square.
一个正方形的周长是120分米，求正方形的面积．
<gadget id="calculator">120 / 4</gadget>
<output>30</output>

<gadget id="calculator">30 * 30</gadget>
<output>900</output>

<result>900</result>