If a parallelogram frame with a base of 20 cm and a height of 15 cm is stretched into a rectangle, the area increases by 60 cm2. What is the width of the rectangle in centimeters?
把一个底为20厘米、高为15厘米的平行四边形框架拉成一个长方形，这时面积增加了60平方厘米．长方形的宽是多少厘米？
<gadget id="calculator">20 * 15</gadget>
<output>300</output>

<gadget id="calculator">300 + 60</gadget>
<output>360</output>

<gadget id="calculator">360 / 20</gadget>
<output>18</output>

<result>18</result>