172. According to the figure below, ray $SI$ hits mirror (1) at angle of incidence $i$. The angle between ray $SI$ and reflected ray from mirror (2), $\gamma = 120°$. If angle $i$ increases by $20°$, how does $\gamma$ change? [Figure: Two mirrors; ray SI incident on mirror (1) at angle $\alpha$; reflected ray hitting mirror (2); $\gamma = 120°$ is marked.]
[(1)] Increases by $40°$.
[(2)] Increases by $20°$.
[(3)] Decreases by $20°$.
[(4)] Remains constant.
\textbf{172.} According to the figure below, ray $SI$ hits mirror (1) at angle of incidence $i$. The angle between ray $SI$ and reflected ray from mirror (2), $\gamma = 120°$. If angle $i$ increases by $20°$, how does $\gamma$ change?
\textit{[Figure: Two mirrors; ray SI incident on mirror (1) at angle $\alpha$; reflected ray hitting mirror (2); $\gamma = 120°$ is marked.]}
\begin{enumerate}
\item[(1)] Increases by $40°$.
\item[(2)] Increases by $20°$.
\item[(3)] Decreases by $20°$.
\item[(4)] Remains constant.
\end{enumerate}