b
\({{\text{V}}_{\text{o}}} = {{\text{i}}_{{{\text{g}}_0}}}\left( {{{\text{R}}_{\text{G}}} + {\text{R}}} \right)\)

\({{\text{i}}_{{g_0}}} = 4 \times {10^{ - 4}} \times 25 = {10^{ - 2}}{\mkern 1mu} {\text{A}}\)

\(\mathrm{V}_{0}=2.5\, \mathrm{V}\)

\(R_{0}+R=\frac{V_{0}}{i_{0}}=\frac{2.5}{10^{-2}}=250\)

\(\Rightarrow \quad \mathrm{R}=200\, \Omega\)