After clarification we see the respective diameters are


We're asked about the ratio

Now we can go through the choices.
A. If a = 4 and b = 6, then cell a is 100 times greater than cell b.

It would be more proper to say the diameter of cell A is 100 times the diameter of cell B, but yes, this is TRUE.
B. If a = 4 and b = 6, then cell b is 100 times greater than cell a.
FALSE. 10 to the minus 4 is 100 times bigger than 10 to the minus 6, so a is bigger.
C. If a = 4 and b = 6, then cell a is 2 times greater than cell b.
FALSE. We already calculated its 100 times bigger.
D. If a = 4 and b = 6, then cell b is 2 times greater than cell a.
FALSE.
Answer: option d.
Step-by-step explanation:
You have the following formul given in the problem:

You know that:
The number of customers serviced in an hour by the technical support representative is 6 costumbers, therefore:

As the problem asked for the probability that a costumber will be on hold less than 30 minutes, we know that:

Substitute the values above into the formula.
Then, you obtain:
or 95%
Given the equation of the parabola

The vertex of this parabola is placed at point (4,3).
If the equation of the parabola is
then

The coordinates of the parabola focus are

Therefore, the focus is placed at point (4,3,75).
Answer: option D, 0.75 in. above the vertex