A square and a rectangle are formed by two wires of the same length. If the length of the rectangle is 13 cm and the width is 5 cm, what is the side length of the square?
用两根同样长的铁丝围成一个正方形和一个长方形．长方形的长13厘米，宽5厘米，那么正方形的边长是多少厘米．
<gadget id="calculator">13 + 5</gadget>
<output>18</output>

<gadget id="calculator">2 / 4</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">18 * (1/2)</gadget>
<output>9</output>

<result>9</result>