The Boolean equation for the circuit given in the figure is

In the above diagram, we have the combination of $\mathrm{NOT}$ gate and $\mathrm{OR}$ gate.

For $\mathrm{NOT}$ gate

$X\mathit{=}\overline{A}\mathit{ }\mathit{ }\mathit{ }\mathit{ }\mathit{ }\mathit{.}\mathit{.}\mathit{.}\left(1\right)$

For $\mathrm{OR}$ gate

$$\begin{gathered} Y=X+B \\ \Rightarrow Y=\overline{A}+B \left[\text{Using} \left(1\right)\right] \end{gathered}$$

Hence, the output expression of the given arrangement of gates is $\left(\overline{A}+B\right)$.