A weather radar sends a pulse towards a rainstorm and detects the reflected pulse 220 μs220\ \mu\mathrm{s}220 μs after transmission. The pulse travels at 3.0 × 108 m/s. The reflecting part of the rainstorm then moves 6.0 km towards the radar. What is the expected echo time after this movement?
An echo time of 240 μs240\ \mu\mathrm{s}240 μs
An echo time of 260 μs260\ \mu\mathrm{s}260 μs
An echo time of 180 μs180\ \mu\mathrm{s}180 μs
An echo time of 200 μs200\ \mu\mathrm{s}200 μs