Answer:
a) 
b)
c)
Step-by-step explanation:
Assuming the following question: Because of staffing decisions, managers of the Gibson-Marimont Hotel are interested in the variability in the number of rooms occupied per day during a particular season of the year. A sample of 20 days of operation shows a sample mean of 290 rooms occupied per day and a sample standard deviation of 30 rooms
Part a
For this case the best point of estimate for the population variance would be:

Part b
The confidence interval for the population variance is given by the following formula:
The degrees of freedom are given by:
Since the Confidence is 0.90 or 90%, the significance
and
, the critical values for this case are:
And replacing into the formula for the interval we got:
Part c
Now we just take square root on both sides of the interval and we got:
The answer should be 7/10!
I'm not sure what you are looking for but I'll answer this question based on what I think is needed.
Given:
Day 1: 130
Day 2: 130 x 4 = 520
Day 3: 520 x 4 = 2,080
The exponential equation of this problem is:
V(n) = 130(4)^n
Where n is the number of days since the video was first shown.
Let us assume that 10 days have past. Total view would be:
V(n) = 130(4)^n
V(10) = 130(4)^10
V(10) = 130(1,048,576)
V(10) = 136,314,880
After 10 days, there are more than 136 Million views of the viral video.