Answer:
Option d)

Step-by-step explanation:
We are given the following in the question:
Three of four people believed that the state of the economy was the country's most significant concern.
They would like to test the new data against this prior belief.
The null hypothesis will state that the three of four people believed that the state of the economy was the country's most significant concern.
The alternate hypothesis will state that this is not true. It states that people believed that the state of the economy was the country's most significant concern is not the same.

We design the null and the alternate hypothesis

The answer is 13. To figure this out I used 10 notebooks sold as a guide. I knew the answer could not be 10, because $27.95/10 was not a number stopping in the hundredths place (or a true money amount).
I tried numbers greater than 10 using a trial and error strategy until I got to 13 notebooks sold and found that it $27.95 was divisible by 13 to get an answer between $2 and $3 ($2.15 exactly).
If you're adding positive numbers together, then the order in which you write or group the addends doesn't matter.
If you're "adding" a negative number to a positive number, it's a little easier to visualize this problem if you write the positive number first, followed by the negative number.
But if you're "adding" -15 to 8, it'd make sense to write the -15 first (because its magnitude is greater) and then the 8: -15 + 8 = -7
Mean: ( 9 + 7 + 6.5 + 7.5 + 7 + 8 + 5 + 6 + 7.5 + 8 ) : 10 = 7.15
Variance:
(Sigma)² = ( 1.85² + 0.15² + 0.65² + 0.35² + 0.15² + 0.85² + 2.15² + 1.15² + 0.35² + 0.85² ) : 10 ≈ 1.15
Answer: C ) 1.15