181. Find the area of a rectangle where the base is twice the height, and the area is numerically equal to the perimeter.
181. If the width is $x$, then the length is $2 x$. Thus, the area is $2 x^{2}$, and the perimeter is $6 x$. According to the condition, $2 x^{2}=6 x$, therefore, $x=3$.