Question

You watch a distant lady driving nails
into her front porch at a regular rate of 2
strokes per second. You hear the sound of the
blows exactly synchronized with the blows
you see. And then you hear one more blow
after you see her stop hammering.
How far away is she? The speed of sound is
340 m/s.
1. 1360 m.
2. 85 m.
3. 680 m.
4. 270 m.
5. 170 m.