Answer:
A sample of at least 68 bulbs is needed to be 96% confident that our sample mean will be within 10 hours of the true mean.
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 M as such

In which
is the standard deviation of the population and n is the size of the sample.
In this problem, we have that:






A sample of at least 68 bulbs is needed to be 96% confident that our sample mean will be within 10 hours of the true mean.
Compound interest formula (annual)
A = P(1 + i)^n
where A = total/final amount
P = principal/initial/beginning amount
i = interest rate
n = number of years
OR if interest was calculated in different time periods such as monthly, semiannually, fortnightly, weekly, daily etc
A = P(1 + i/k)^n
where k = number of periods in that year
n = kt = number of periods * number of years
e.g. if interest was calculated monthly for 2 years
k would be 12 & n would be 12*2 = 24
The bank will claim the lien. A.K.A, collateral