7. Now, we need to manufacture a cone with a base diameter of $4 \mathrm{~cm}$ and a slant height of $6 \mathrm{~cm}$. We will use a rectangular piece of material to make its lateral surface. The minimum length and width dimensions of such a rectangular material are $\qquad$ .
$12 \mathrm{~cm} \times 9 \mathrm{~cm} ;$