If the area of a rectangle is 30 square centimeters, if its length and width are doubled, how many square centimeters will the area increase?
一个长方形的面积是30平方厘米，把它的长和宽都扩大到它们各自的2倍，面积增加了多少平方厘米．
<gadget id="calculator">2 * 2 * 30</gadget>
<output>120</output>

<gadget id="calculator">120 - 30</gadget>
<output>90</output>

<result>90</result>