Roberta Coy makes custom mooring covers for boats. Each mooring cover is hand sewn to fit a particular boat. If covers are made for two or more identical boats, each successive cover generally requires less time to make. Coy has been approached by a local boat dealer to make mooring covers for all of the boats sold by the dealer. Coy has developed the following cost schedule for mooring covers made to fit 17-foot outboard power boats.

Mooring Covers Made Total Cost of Covers

1 $460

2 860

3 1,220

4 1,540

5 1,830

Compute the average cost if two mooring covers are made.