Answer:
The journal entries are as follows:
(1) (i) On October 10, 2018 
Merchandise inventory A/c (3,500 × $17) Dr. $59,500
         To Accounts payable (Piranha)                             $59,500
(To record the purchase of books)
(ii) On October 13, 2018 
Accounts payable A/c (100 × $17) Dr. $1,700
         To merchandise inventory                     $1,700
(To record the purchase return of book)
(2) (i) On October 10, 2018 
Accounts receivable A/c Dr. $59,500
          To sales 
(To record the sales of book)
Cost of goods sold A/c Dr. $35,700
             To merchandise inventory    $35,700
(To record the cost of goods sold of book)
(ii) On October 13, 2018 
Sales return and allowances A/c Dr. $1,700
               To accounts receivable                  $1,700
(To record the sales return of book)
Merchandise inventory A/c Dr. $1,020
            To cost of goods sold               $1,020
(To record the cost of good return)