The most likely measurement for a two-story building would be 20 feet. 6 inches, 25 inches, and 6 feet all are way too short for a two-story building.
For this case, we must indicate which of the given functions is not defined for
By definition, we know that:
has a domain from 0 to infinity.
Adding or removing numbers to the variable within the root implies a translation of the function vertically or horizontally. For it to be defined, the term within the root must be positive.
Thus, we observe that:
is not defined, the term inside the root is negative when
.
While
if it is defined for 
, your domain is given by all real numbers.
Adding or removing numbers to the variable within the root implies a translation of the function vertically or horizontally. In the same way, its domain will be given by the real numbers, independently of the sign of the term inside the root.
So, we have:
with x = 0:
is defined.
with x = 0:
in the same way is defined.
Answer:

Option b
D. The set of all points in a plane that are equidistant from a fixed point.
It depends on what happens to the price of the item during the sale which is not stated in your problem. So if it cost 6 dollars and goes on sale it should be 6 dollars.