The output of the given combination gates represents:

By De Morgan's theorem, we have

Here the output of $A$ and $B$ gives $\overset{¯}{A}$ and $\overset{¯}{B}$. This output is fed as inputs to NAND gate and the output is $A \cdot B$, when when again fed as input to NAND gate to get output as $\overset{¯}{A \cdot B}$.