I will convert the unit of distance to SI unit for simplification.
1 mile = 1.6 km
Therefore, 0.245 mile = 0.245×1.6 = 0.392 km = 392 meters
Radio waves travels back after bouncing off from car.
Therefore, total distance traveled by radio waves = 2×392 = 784 meters.
Speed of radio waves = 3×10⁸ m/s
Therefore, time take by radar beam to travel to a car and back = 784/3×10⁸
=2.61×10⁻⁶sec