A Bat, Flying Toward the East at 2

Short Answer

A bat, flying toward the east at 2.0 m/s, emits a shriek that is reflected back to it from a
wall that is 20.0 m in front of the bat at the instant the shriek is emitted. Sound travels at
340 m/s in the air. How many milliseconds after emitting the shriek does the bat hear the
reflected echo from the wall?