To calculate circumference, you must use the equation (65)(2)(Pi) which would be 408.2pm. (IF YOU COUNT PI AS 3.14)
All you have to do is plug in the given values into the given equation and evaluate.
The expression is,

But we have to analyze the problem carefully. This is a natural phenomenon that can be modelled by a decay function. The reason is that, after every hour we expect the medicine in the blood to keep reducing.
Therefore we use the decay function rather. This is given by,

where,


and

On substitution, we obtain;


Now, we take our calculators and look for the constant

,then type e raised to exponent of -1.4. If you are using a scientific or programmable calculator you will find this constant as a secondary function. Remember it is the base of the Natural logarithm.
If everything goes well, you should obtain;

This implies that,

Therefore after 10 hours 24.66 mg of the medicine will still remain in the system.
Distance = rate * time (I will abbreviate as d = rt)
d = rt, so r = d/t
r = 20mi/24min
= 0.833333 mi/min.
d = rt again for the new time
d = 0.8333333 mi/min * 6 min = 5 miles
Hi there!
The answer would be B. The number 3 was rolled 5 times in 36 trials.
This shows that out of all 36 times the dice was rolled the number 3 faced upwards 5 times.
Hope this helps !