Question 972294
Yes to both.
Exactly two would be as you have written , and the probability = approx .22, which makes intuitive sense.

A check is that
(9/12)*(8/11)*(3/10)*(2/9) is one of six ways you can choose two working computers out of 4.  The other five ways change the numerator for the denominator, but the products are the same, and they add up to the same number.

For C, yes, do the null.  It is a lot easier.