Two cars A and B are in the same direction with velocities v1 and v2

Two cars A and B are in the same direction with velocities v1 and v2 (v1>v2). When the car A is at a distance d behind the car B, the driver of the car A applies the brake producing uniform retardation a, There will be no collision when

Question : Two cars A and B are in the same direction with velocities v1 and v2 (v1>v2). When the car A is at a distance d behind the car B, the driver of the car A applies the brake producing uniform retardation a, There will be no collision when

(a) d <\dfrac{\left( V_{1}-V_{2}\right) }{2a}

(b) d >\dfrac{\left( V_{1}^{2}-V_{2}^{2}\right) }{2a}