What do you mean with P(2 by 1) ??
Is that a vector with 2 rows and 1 column?
If it is then there is no way P.X is defined with X being a 2 row 1 column vector.
2x1 2x1 is not defined.
P must be always a 2x2 matrix like in a and b.
Please explain better what do you mean for question c).