\textbf{166.} Inside a container, 200 grams of ice is at $-10$ degrees Celsius. At least how many grams of water at $20^\circ$C must be added to melt all the ice? (Heat exchange occurs only between water and ice, $L_f = 336\,\frac{J}{g}$, $C_{\text{ice}} = 2\,\frac{J}{g \cdot k}$, $C_{\text{water}} = \frac{1}{2}$)
\hspace{1cm} (1) $50$ \hspace{2cm} (2) $200$ \hspace{2cm} (3) $850$ \hspace{2cm} (4) $1200$