Explanation

(b)
Let the standard equation of ellipse is $\frac{x^{2}}{a^{2}} + \frac{y^{2}}{b^{2}} = 1\ (a > b)$
Minor axis $= 2b = 8 \Rightarrow b = 4$
And eccentricity $= e = \frac{\sqrt{5}}{3}$
Now, $b^{2} = a^{2}(1 - e^{2})$
$\Rightarrow (4)^{2} = a^{2}\left( 1 - \frac{5}{9} \right)$
$\Rightarrow 16 = a^{2}\left( \frac{4}{9} \right)$
$\Rightarrow a^{2} = 36 \Rightarrow a = 6$
Length of major axis $= 2a = 12$