Answer 1

\[\text{ Let r be the radius of the circular cylinder }  . \]
\[\text{ Height, h = 10 . 5 cm } \]
\[\text{ Area of the curved surface, }  S_1 = 2\pi r h\]
\[ \text{ Sum of the areas of its two circular faces, }  S_2 = 2\pi r^2 \]
\[ \text{ According to question } : \]
\[ 3 S_2 = 2 S_1 \]
\[3 \times 2 \pi r^2 = 2 \times 2\pi rh\]
\[ 6r = 4h\]
\[ 3r = 2h\]
\[ r = \frac{2}{3} \times 10 . 5 cm\]
\[ = 7 cm\]