The length of a rectangle is 15 cm and its width is 3 times that of the rectangle. What is the area of the rectangle?
一个长方形长15厘米，是宽的3倍，这个长方形的面积是多少．
<gadget id="calculator">15 / 3</gadget>
<output>5</output>

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

<result>75</result>