The length of a rectangle is three times its width, and the length of the diagonal is 30 cm. What is the area of the rectangle in square centimeters?
一个长方形的长是宽的3倍，对角线长30厘米，这个长方形的面积是多少平方厘米．
<gadget id="calculator">3 * 90</gadget>
<output>270</output>

<result>270</result>