15/60=1/4=0.25
0.25*100=25
15/60 in % is 25%
Area of a circle = pi • r^2
We need to isolate for r.
A/pi = r^2
r = sqrt(A/pi)
r = sqrt(30.8/pi)
r = 3.1311251164
Diameter = 2r
Diameter = 6.26225023
Diameter = 6.3 m
You're correct, the answer is C.
Given any function of the form

, then the derivative of y with respect to x (

) is written as:

In which

is any constant, this is called the power rule for differentiation.
For this example we have

, first lets get rid of the quotient and write the expression in the form

:

Now we can directly apply the rule stated at the beginning (in which

):

Note that whenever we differentiate a function, we simply "ignore" the constants (we take them out of the derivative).
The answer would be D because when you divide 10 by 4 you take one fourth out of ten