(a)
Since X can only assume whole values, it is a discrete random variable.
(b)
The sum of all probabilities in the table must be equal to 1, so we have:
(c)
The values of x smaller than 5 in the table are 3 and 4, so we have:
(d)
For x between 4 and 6, we have:
(e)
Looking at the table, for x = 3 we have: