a) There are 6 lines: PQ, PR, PS, QR, QS, RS if no 3 points are collinear.
b) If we remove P we have QR, QS, RS as the remaining non-collinear lines. So the collinear lines would be:
PQR, one line contains PQR in the order PQR, QPR, QRP, PRQ, RPQ, RQP
PQS, one line contains PQS in the order PQS, QPS, QSP, PSQ, SPQ, SQP
PRS, one line contains PRS in the order PRS, RPS, RSP, PSR, SPR, SRP
In each case the non-collinear point can form 3 lines with the collinear points. That makes 4 lines in all. For example, if the collinear points are P, R and S, there is one line for the six P, R, S configurations and PQ, QR and QS are the other 3 lines.
There are many configurations of points depending on which points are collinear. In the example, there would be 4 lines for each of the 6 different configurations.