$1)$ For part $\backslash ($ A $\backslash )$ the center tapped secondary transformer behaves like two $\backslash ($ A C $\backslash )$ sources connected in series.

$2)$ For part B you have to do the transformer analysis. As the voltages are the same for each half of the secondary transformer you know that it is center tapped with the same number of windings on each half.