Answer:
0.3108 is the probability that the sample mean is between 7.8 and 8.2 minutes.
Step-by-step explanation:
We are given the following information in the question:
Mean, μ = 8 minutes
Standard Deviation, σ = 2.5 minutes
Sample size, n = 25
We are given that the distribution of time spent is a bell shaped distribution that is a normal distribution.
Formula:

Standard error due to sampling =

P(sample mean is between 7.8 and 8.2 minutes)

0.3108 is the probability that the sample mean is between 7.8 and 8.2 minutes.
You see, the thing is, you dont
You can do this by first finding the y intercept which is the point where x = 0
-3(0) + y = 2
so y intercept is the point (0,2)
Now find the x intercept by putting y = 0
-3x = 2
x = -2/3
So we have 2 points (-2/3, 0) and (0,2) Draw a line through these 2 points and you have the required graph.
It would be (0,-3) and (2,3). You can see that they have a bigger distance compared to the other points being compared.