Manley's deduction for bad debt expense this year would be $7,300.
To determine this, you need to calculate the net increase in the allowance for doubtful accounts:
Net increase in allowance = Ending balance of doubtful accounts - Beginning balance of doubtful accounts
Net increase in allowance = $20,000 - $13,700
Net increase in allowance = $6,300
Then, you can calculate the amount of bad debt expense that was actually recorded during the year:
Bad debt expense recorded = $21,000
Finally, you can calculate the deduction for bad debt expense:
Deduction for bad debt expense = Bad debt expense recorded - Net increase in allowance
Deduction for bad debt expense = $21,000 - $6,300
Deduction for bad debt expense = $7,300
Therefore, Manley's deduction for bad debt expense this year would be $7,300.