$($a$)$ Using Boolean algebraic techniques, simplify the following expression:

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$Y=A*B\frac{*}{b}ar(C)\frac{*}{b}ar(D)\frac{+}{b}ar(A)*B\frac{*}{b}ar(C)\frac{*}{b}ar(D)\frac{+}{b}ar(A)*B*C\frac{*}{b}ar(D)+A*B*C\frac{*}{b}ar(D)$

$($b$)$ Write the Boolean expression for the logic circuit shown in Fig $7\mathrm{.}0.$

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