Answer:
The Journal entries are as follows:
(i) On April 1,
Notes receivables A/c  Dr. $15,000
To service revenue               $15,000
(Being notes receivables accepted)
(ii) On October 1,
Cash A/c           Dr. $15,600
To Notes receivables            $15,000
To Interest revenue              $600
(Being cash and interest on note)
Workings:
Interest revenue = 15,000 × 8% × (6 ÷ 12)
              = $600