$1($b$)$ i$)$ For the system represented by the following equations, find the transfer $[2+3]$ function $x\frac{s}{U}(s)$ by drawing the signal flow graph and applying Mason's gain formula.

$x=x_1+{}_{3}u$

$x_1^{}=-{}_1{x}_1+x_2+{}_{2}u$

$x_2^{}=-{}_2{x}_1^{}+{}_{1}u$

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