Answer:
1,404,000 unique passwords are possible.
Step-by-step explanation:
The order in which the letters and the digits are is important(AB is a different password than BA), which means that the permutations formula is used to solve this question.
Permutations formula:
The number of possible permutations of x elements from a set of n elements is given by the following formula:

In this question:
2 digits from a set of 10(there are 10 possible digits, 0-9).
3 characters from a set of 26. So

1,404,000 unique passwords are possible.
I believe it is the first one. A.
Answer:

Step-by-step explanation:
Normal distribution, is a "probability distribution that is symmetric about the mean, showing that data near the mean are more frequent in occurrence than data far from the mean".
The t distribution or Student’s t-distribution is a "probability distribution that is used to estimate population parameters when the sample size is small (n<30) or when the population variance is unknown".
The shape of the t distribution is determined by its degrees of freedom and when the degrees of freedom increase the t distirbution becomes a normal distribution approximately.
Data given
Confidence =0.99 or 99%
represent the significance level
n =16 represent the sample size
We don't know the population deviation 
Solution for the problem
For this case since we don't know the population deviation and our sample size is <30 we can't use the normal distribution. We neeed to use on this case the t distribution, first we need to calculate the degrees of freedom given by:

We know that
so then
and we can find on the t distribution with 15 degrees of freedom a value that accumulates 0.005 of the area on the left tail. We can use the following excel code to find it:
"=T.INV(0.005;15)" and we got
on this case since the distribution is symmetric we know that the other critical value is 
Answer:
9. a) 18 b) 4
10. a) 67.5g b) $75
Step-by-step explanation:
9. a) 3*n=(9*6), n=18
b) cross multiply and you will get 15n=60, n=4
10 a) 15% of 450=(15*450)/100=67.5
b) 125% of $60=(125*60)/100=75