The length of a rectangle is 15 cm and its length is three times its width. What is the area of this rectangle in square centimetres.
一个长方形的长是15厘米，长是宽的3倍．这个长方形的面积是多少平方厘米．
<gadget id="calculator">15 / 3</gadget>
<output>5</output>

<gadget id="calculator">15 * 5</gadget>
<output>75</output>

<result>75</result>