RATE SHEET

CAN SOMEONE HELP ME?
I need a formula and i can’t figure it out.. Im making a rate sheet with premiums.
example: A premium of $616.00 for the first $15,000. If i was to add ($22/1000 excess of $15,000) how could i get it to figure that out for me.

Coverage Single Unit Premium

$200,000 $880.00 $616.00
The first $15,000 ($22/1000 excess of $15,000)

If somone could help me that would be great.