\[\boxed{\mathbf{904\ (904).\ }Еуроки\ - \ ДЗ\ без\ мороки}\]
\[S = 63;\ \ q = \frac{4}{9}\]
\[S = \frac{b_{1}}{1 - q}\ \]
\[b_{1} = S \cdot (1 - q) =\]
\[= 63 \cdot \left( 1 - \frac{4}{9} \right) = 63 \cdot \frac{5}{9} =\]
\[= 7 \cdot 5 = 35.\]
\[Ответ:b_{1} = 35.\]