(c)
$\tan{(A - B) = \tan{\frac{\pi}{4} = 1}}$
$\Rightarrow \ \ \frac{\tan{A - \tan B}}{1 + \tan{A\tan B}} = 1$
$\Rightarrow \tan{A - \tan{B - \tan{A\tan{B = 1}}}}$ …(i)
Now, $y = \left( 1 + \tan A \right)(1 - \tan B)$
$= \left( 1 - \tan{B + \tan{A - \tan{A\tan B}}} \right)$
$= (1 + 1) = 2$ [from Eq. (i)]
$\therefore\ \ \ \ (y + 1)^{y + 1} = (2 + 1)^{2 + 1} = 3^{3} = 27$