Draw a signal flow graph for the following set of algebraic equations
\[\begin{array}{l}
y_{2}=a \; y_{1}-g \; y_{3} \\
y_{3}=e \; y_{2}+c \; y_{4} \\
y_{4}=b \; y_{2}-d \; y_{4}\end{array}\]
Hence, find the gains $\frac{y_{2}}{y_{1}}$ and $\frac{y_{3}}{y_{1}}$
