The escape velocity at the event horizon of a black hole is 3×10^8 m/s, i.e., the velocity of light. What is the mass of the black hole if the distance from its centre to the event horizon is 18km?
(a) 12.15 x 10^-30 kg
(b) 12.15 x 10^30 kg
(c) Infinity
(d) Cannot be determined