For this case we have that by definition, the circumference of a circle is given by:

Where:
d: Is the diameter of the circumference
According to the data we have to:

Substituting:

Rounding out we have that the diameter is: 80
Answer:
Option B
Here is the equation you should use.
2(x+7) = -36
When the black chip is drawn, there is already one less chip in the bag; keep this in mind..
the probability of getting a black chip out of the bag is 10/25 or 2/5
now since there is one less chip, there is a total of 24 chips now..
so now the probability of getting a red chip is 5/24
then you would multiply the two events together and get:
2/5 x 5/24....solve
The answer is 17.5!! goodluck