A rectangle with a width of $2 \mathrm{~cm}$ and a length of $18 \mathrm{~cm}$ has the same area as a square with a side length of
(A) $6 \mathrm{~cm}$
(B) $12 \mathrm{~cm}$
(C) $9 \mathrm{~cm}$
(D) $10 \mathrm{~cm}$
(E) $8 \mathrm{~cm}$
A rectangle with a width of $2 \mathrm{~cm}$ and a length of $18 \mathrm{~cm}$ has area $2 \times 18=36 \mathrm{~cm}^{2}$.

The area of a square with side length $s \mathrm{~cm}$ is $s \times s \mathrm{~cm}^{2}$.

The area of the square is also $36 \mathrm{~cm}^{2}$ and since $6 \times 6=36$, then the side length of the square, $s$, is $6 \mathrm{~cm}$.

ANSWER: (A)