I know this is a stretch, but maybe the thickness of a nail?
Answer:
The correct answer is 20%
Hope this helped! :)
^-^
For this case we must find the value of the variable "x" of the following equation:

We multiply by 3 on both sides of the equation:

We divide between 2 on both sides of the equation:

We subtract 7 on both sides of the equation:

Answer:
Option B