They use x-rays to diagnose broken bones

With the given values of
, we have

Try dealing with the powers of 10 first: On the right, we have

Meanwhile, the other values on the right reduce to

Then taking units into account, we end up with the equation

Now we solve for
:


or, if taking significant digits into account,

b. The guitar represents half of the wave length. So the full wave length is 2x0.9m = 1.8m.
Using the given equation, v= λ ∙ f,
the wave is moving back and forth along the string at 1.8 ∙ 256
= 460.8m/s
c. Sound waves travel at 6,000 m/s.
Using the given equation, v=d/t, or d=vt,
train's vibration in 3 seconds travels 6000*3
=18,000m or 18km