Answer and Explanation:
The journal entries are shown below:
a. On November
Warranty expense Dr $29,840 (37,300 units × 4% × $20)
 To Estimated warranty payable $29,840
(Being the warranty expense is recorded)
For recording this we debited the expense as it increase the expense and credited the estimated warranty payable as it increased the liabilities 
On December 
Warranty expense Dr $31,440 (39,300 units × 4% × $20)
 To Estimated warranty payable $31,440
(Being the warranty expense is recorded)
For recording this we debited the expense as it increase the expense and credited the estimated warranty payable as it increased the liabilities 
For cost incurred 
Accrued Warranty Expense $24,740
 To Cash $24,740
(Being the cash is paid) 
For recording this we debited the expense as it increase the expense and credited the cash as it reduced the assets