Answer: The answer is $429,200.
Step-by-step explanation: What you need to do is to simply prepare a movement schedule of the transactions given in the question, as follows:
Accounts receivable - opening balance $21,600
Cash sales during the year (addition) $438,000
Cash collections XXXX
Accounts receivable - ending balance $30,400
To find the cash collection, simply $21,600 + $438,000 - XXXX = $30,400
$459,600 - XXXX = $30,400
XXXX = $459,600 - $30,400
XXXX = $429,200
Note that if it is indirect cash flows method, the uncollectible account would have been considered as non-cash item and added back to net income.