A transmission line terminates in two branches, each of length $\lambda / 4$, as shown. The branches are terminated by $50 \; \Omega$ loads. The lines are lossless and have the characteristic impedances shown. Determine the impedance $Z_{i}$ as seen by the source.
- $200 \; \Omega$
- $100 \; \Omega$
- $50 \; \Omega$
- $25 \; \Omega$