Answer:
Diverge
Step-by-step explanation:
(a)
1st year: 
2nd year: 
3rd year: 
4th year: 
5th year: 
(b) The sequence is divergent, because if we take the derivative of the function with respect to n year:

This is a positive, meaning the slope of the function is positive. If we take the second derivative using product rule

This is also positive when n > 0. Therefore, the slope is positive and increasing. This means the sequence diverges.
2000(3/5)
6000/5
1200
So 1200 doctors used brand X
18 what is this for exactly..?
To solve this problem you must apply the proccedure shown below:
You must switch the variables, and then, you must solve for
, as following:

Therefore, as you can see, the answer is: 
The answer is A: 5
Any answer with 0 doesn't work because then the denominator would be 0 as well, and negative 5 does not make the numerator equal to 0.