From the given information, boys and girls should be sitting alternately.
From (a) and (c), we can say that C and B are opposite each other, and A and D are opposite each other.
From (b) and (c), and the above results, we have the following arrangement:

Using (d) since D is sitting three places away to the right of P, we can decide the location of P.

From (c), R must be to the immediate left of A and C is to the immediate left of R.
The final arrangement will be as follows:

Q is to the immediate left of C.