Explanation

(a)
Let $\alpha$ and 3 are the roots of the equation $x^{2} + ax + 3 = 0$
$\therefore\ \ \ 3\alpha = 3\ \ \ \ \ \ \Rightarrow \ \ \ \alpha = 1$
And $3 + \alpha = - a\ \ \ \ \Rightarrow \ \ \ a = - 4$
Again, let $\beta$ and $3\beta$ are the roots of the equation
$x^{2} + ax + b = 0$
$\therefore\ \ \beta + 3\beta = 4\beta = - a\ \ \ \Rightarrow \ \ \ \beta = 1$
And $\beta.3\beta = b\ \ \ \Rightarrow \ \ \ b = 3$