its part a is correct but part b is wrong . please tell me about the journal entries of part b.

On January 6, Duffy Dog Limited sold merchandise on account to Singh Inc. for $45,600, terms n/30. The merchandise originally cost Duffy Dog $28,500. On January 25 , Singh paid the amount due. Both Duffy Dog and Singh use a perpetual inventory system. Prepare the entries on Duffy Dog's books to record the sale and related collection. (List all debit entries before credit entries, Credit. account tidies ore outomaticnlly indented when amount is entered. Do not indent manually. If no entry bs required, select "No Entry" for the occount tities and enter 0 for the amounts.) Di Prepare the entries on Singh's books to record the purchase and related payment. (List oll debit entries before credit entries. Credit occount titles are outomatically indented when amount is entered. Do not indent manually. If no entry is required, select "No Entry" for the occount bitles and enter Ofor the amounts.)