The length and width of a rectangle are both prime numbers in meters, and the length and width are not equal. Its perimeter is 20m. What is the area of the rectangle in square meters?
一个长方形的长和宽都是以米为单位的质数，且长与宽不相等，它的周长是20m，这个长方形的面积是多少平方米？
<gadget id="calculator">7 * 3</gadget>
<output>21</output>

<result>21</result>