\[x_{7} = \frac{3}{16};\ \ \ \ \ q = \frac{1}{2}:\]
\[x_{7} = x_{1}q^{6}\text{\ \ \ \ }\]
\[x_{1} = \frac{x_{7}}{q^{6}} = \frac{3 \cdot 6}{16 \cdot 1} = 12.\]
\[Ответ:12.\]