Answer
(c) $R_{A}=3R_{B}$
Work Step by Step
Schwarzschild radius of the black hole is given by :-
$R=\frac{2GM}{c^{2}}$
where M is mass of the black hole
so, R is directly proportional to M.
So if the mass of black hole A is three times the mass of black hole B, then the Schwarzschild radius of A is three times that of black hole B.
i.e. $R_{A}=3R_{B}$
