p = number of items sold (note: this is not the profit)
1 item sells for $855, so p items sell for 855p dollars
Subtract off the cost of 6780 and we have the expression 855p-6780 which is the profit for that given month.
Now plug in p = 250 because 250 items were sold in that given month
855*p - 6780 = 855*250 - 6780 = 206,970
The company earns $206,970 in profit for that month. Apply 15% to this value
15% of 206,970 = (15/100)*206,970 = 0.15*206,970 = 31,045.50
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Answer: $31,045.50 which is choice C