Gstr 3b and gstr 1

Suppose A is buying goods for rs 1L per day from B for 15 days and sale that for the same amount to his customers. He makes the payment of 1L next day. On 16th day bill the commission of 3% ie 45000 will be deducted from 1L of that day n he will pay 55000 next day.
How to treat these transactions in gst returns of A?