I think that it could possibly be 12 feet but at the same time I'm not sure
9 tenths - 3 tenths = 6 tenths. this is true the same way that 9 minus 3 = 6. In reality the tenths make both numbers decimals, but in this case the "tenths" is just a classification of the number and it doesn't effect the answer.
Answer:
a)
And rounded up we have that n=4906
b) For this case since we don't have prior info we need to use as estimatro for the proportion 
And rounded up we have that n=6724
Step-by-step explanation:
We need to remember that the confidence interval for the true proportion is given by :
Part a
The estimated proportion for this case is 
Our interval is at 90% of confidence, and the significance level is given by
and
. The critical values for this case are:
The margin of error for the proportion interval is given by this formula:
(a)
The margin of error desired is given
and we are interested in order to find the value of n, if we solve n from equation (a) we got:
(b)
Replacing we got:
And rounded up we have that n=4906
Part b
For this case since we don't have prior info we need to use as estimatro for the proportion 
And rounded up we have that n=6724
24- 1,2,3,4,6,8,12,24
64-1,2,4,8,16,32,64
88-1,2,4,8,11,22,44,88
Here are all the factors.^^
The common factors are 1,2,3,4,6
Hope this helps!
I think it is 16 I am not sure because I did not do it I am just guessing