Which one of the following is a correct statement about corporations?
a. most businesses in the united states are corporations.
b. a corporation is treated as though it were an actual person.
c. if a corporation fails, the stockholders lose all their money.
d. stockholders hire the people who manage a corporation.
the money a bank pays depositors for the right to use their money is called
a. reserve.
b. interest.
c. investment.
d. credit.

In the first question, the correct answer is C - If a corporation fails, the stockholders lose all their money. 

Corporations are usually, if not all of the time, being shared between different investors and stockholders. All of these people invested a portion of their money for a percentage of the company. 

The correct answer for your second question is D - a credit.

How do you calculate the mean (average) ?
Isn't it just

  Mean = (total points of all the tests) divided by (number of tests)  ?

Let's work with that.

Multiply each side of that formula by (number of tests), and you have

       Total points of all the tests  =  (Mean) times (number of tests).

In this problem, you know the mean, and you know the number of tests,
so you can easily calculate the total points.