This is a bit of a guess, but I think probably a) +4 and also a) -215
Answer:
The answer I got was 7 7/10
(sorry if wrong!)
6= w/8
is
w= -48
that should be if not sorry DX
Answer:
The sample size required is at least 171
Step-by-step explanation:
We have that to find our
level, that is the subtraction of 1 by the confidence interval divided by 2. So:

Now, we have to find z in the Ztable as such z has a pvalue of
.
So it is z with a pvalue of
, so 
Now, find the margin of error M as such

In which
is the standard deviation of the population and n is the size of the sample.
What sample size is required?
A samle size of at least n is required, in which n is found when 
So






Rouding up
The sample size required is at least 171
2 ratio 3,so, 2+3=5
15/5=3 add and then division