By using the equation speed = distance/time we can solve for distance. The speed is 4 m/s and the time is 12 seconds. We need to rearrange the equation to Speed * Time = distance. 4(12) = 48; 48 = distance. The cliff is 48 meters high.
There's no rule like that. A glass mirror is opaque but reflects
more light than a clean transparent glass window does.
On the other hand, a material that's transparent but shiny may
reflect more light than an opaque material that's painted black.
You can't give any general rule.
If a photon has a wavelength of about 10^-10 meters, it would be certainly in the X rays region and it would have a frequency of 2.99792458x10^18 Hz, that you can easily calculate using the relation that states that the product of the wavelength and the frequency of an electromagnetic wave aka light is always equal to 299,792,458 m/s which is the exact value of the speed of light!