Dispensing doctors

case number 1-

If a maufacturer of medicines  having Gst no. sells products @ Rs. 30 (MRP of Rs.100)  directly to a dispensing doctor who is not registered for GST .

how much Gst have to paid by Doctor  .  ??

case number 2-

if a maufacturer of medicines  having Gst no. sells products @ Rs. 30 (MRP of Rs.100)  directly to a dispensing doctor who is  Registered under composite scheme ( 75 lakh turnover)   .

how much Gst have to paid  by doctor ??

case number 3-

if a maufacturer of medicines  having Gst no. sells products @ Rs. 30 (MRP of Rs.100)  directly to a dispensing doctor who is  registered under GSt & having turnover more than 75 Lakh  .

how much Gst have to paid  by doctor ??