You are the manager of World Wide Athlete, a chain of six sporting goods shops in your area. The shops sell $12$ racing bikes per week at a retail price of $$679\mathrm{.}99.$ Recently, you put the bikes on sale at $$599\mathrm{.}99.$ At the sale price, $15$ bikes were sold during the oneweek sale.

a$.$ What was your markdown percent on the bikes?