Determine the cash collected from customers by jones

Question

The following information was taken from the 2011 financial statements of Jones Corporation:

Accounts receivable, January 1, 2011         $30,000
Accounts receivable, December 31, 2011      40,000
sales(All credit sales)                              4,80,000

Required
a. Determine the cash collected from customers by Jones Corporation in 2011.

b. Comment on why cash collected from customers differed from sales.