Answer:
a.- 0.000038 m/año
Step-by-step explanation:
This is a very little number, if it is checked as a number. But, imagine the hole rock, like in this example, 3 ft each side, is a very big and weight rock.
If it is divided 0.1 Kg/m2/year into 2600 kg/m3 it will be 0.000038 m/year.
This number actually shows the strong of the nature to stay practically the same, it it will change in a very long period.
The lowering rate in layers of soil is a common process in which the layers of the bottom can lost air, force or they rearrange by a chemical reaction.
Hope this info is useful