\textbf{135-} The length of the common internal tangent of two circles with internal radii $3/5$ cm and the area of the region bounded between them is $21\pi$ square centimeters. The diameter of the smaller circle is how many centimeters?
\[
\text{(1)}\ 1/25 \qquad \text{(2)}\ 1/75 \qquad \text{(3)}\ 2/25 \qquad \text{(4)}\ 2/75
\]