She purchased more than 2, but less than 8 items.
The force for the case 1 is 64 pounds and the distance is 9 feet, it is:

Now, if the force is 36 pounds, let solve for the distance:

Hence the answer is 12 feet.
Answer:
a) 
b) First we need to calculate the variance given by this formula:

And the deviation would be:

c) 
And using the cdf we got:

d) 
Step-by-step explanation:
For this case we define the random variable X who represent the customers charge, and the distribution for X on this case is:

Part a
For this case the average is given by the expected value and we can use the following formula:

Part b
First we need to calculate the variance given by this formula:

And the deviation would be:

Part c
For this case we want to find the percent between 600 and 889, so we can use the cumulative distribution function given by:

And we can find this probability:

And using the cdf we got:

Part d

And using the cdf we got:
