Let's use variables to represent the number of $1000 and $500 bills used.
Let x be the number of $1000 bills used.
Then 16 - x is the number of $500 bills used.
The total amount paid is the sum of the values of the bills used:
$1000(x) + $500(16 - x) = $3200
Simplifying and solving for x:
$1000x + $8000 - $500x = $3200
$500x = $4800
x = 9.6
We can't have a fraction of a bill, so we'll round down to 9 $1000 bills.
Then the number of $500 bills used is:
16 - x = 16 - 9 = 7
Therefore, 9 $1000 bills and 7 $500 bills were used to pay the $3200 restaurant bill.