You would get 13.7
mi/51mm=3.5mm/13mm
by solving it you will B13.7mm
A) 
The energy of an x-ray photon used for single dental x-rays is

The energy of a photon is related to its wavelength by the equation

where
is the Planck constant
is the speed of light
is the wavelength
Re-arranging the equation for the wavelength, we find

B) 
The energy of an x-ray photon used in microtomography is 2.5 times greater than the energy of the photon used in part A), so its energy is

And so, by using the same formula we used in part A), we can calculate the corresponding wavelength:

Answer:
<em>1.Magnetic Force - Used in cranes to separate metal junk from junkyards.</em>
<em>2.Frictional Force- Helps us to walk.</em>
The answer is B. A frame of reference that is accelerating.