Simplifique $$$\overline{\left(\overline{A} + B\right) \cdot \left(\overline{B} + C\right)}$$$

Aplique o teorema de De Morgan $$$\overline{x \cdot y} = \overline{x} + \overline{y}$$$ com $$$x = \overline{A} + B$$$ e $$$y = \overline{B} + C$$$:

$${\color{red}\left(\overline{\left(\overline{A} + B\right) \cdot \left(\overline{B} + C\right)}\right)} = {\color{red}\left(\overline{\overline{A} + B} + \overline{\overline{B} + C}\right)}$$

Aplique o teorema de De Morgan $$$\overline{x + y} = \overline{x} \cdot \overline{y}$$$ com $$$x = \overline{A}$$$ e $$$y = B$$$:

$${\color{red}\left(\overline{\overline{A} + B}\right)} + \overline{\overline{B} + C} = {\color{red}\left(\overline{\overline{A}} \cdot \overline{B}\right)} + \overline{\overline{B} + C}$$

Aplique a lei da dupla negação (involução) $$$\overline{\overline{x}} = x$$$ com $$$x = A$$$:

$$\left({\color{red}\left(\overline{\overline{A}}\right)} \cdot \overline{B}\right) + \overline{\overline{B} + C} = \left({\color{red}\left(A\right)} \cdot \overline{B}\right) + \overline{\overline{B} + C}$$

Aplique o teorema de De Morgan $$$\overline{x + y} = \overline{x} \cdot \overline{y}$$$ com $$$x = \overline{B}$$$ e $$$y = C$$$:

$$\left(A \cdot \overline{B}\right) + {\color{red}\left(\overline{\overline{B} + C}\right)} = \left(A \cdot \overline{B}\right) + {\color{red}\left(\overline{\overline{B}} \cdot \overline{C}\right)}$$

Aplique a lei da dupla negação (involução) $$$\overline{\overline{x}} = x$$$ com $$$x = B$$$:

$$\left(A \cdot \overline{B}\right) + \left({\color{red}\left(\overline{\overline{B}}\right)} \cdot \overline{C}\right) = \left(A \cdot \overline{B}\right) + \left({\color{red}\left(B\right)} \cdot \overline{C}\right)$$