Xiao Ming surrounds a rectangle with a width of 5 cm with a rope 30 cm long. What is the area of this rectangle in square centimetres.
小明用30厘米长的绳子围一个宽为5厘米的长方形．这个长方形的面积是多少平方厘米．
<gadget id="calculator">30 / 2</gadget>
<output>15</output>

<gadget id="calculator">15 - 5</gadget>
<output>10</output>

<gadget id="calculator">10 * 5</gadget>
<output>50</output>

<result>50</result>