It takes 81 bricks to place along the walkway of the house. if the bricks cost $.15 a piece. how much would the brick border cost?

Martha is training for a duathlon, which includes biking and running. she knows that yesterday she covered a total distance of over 55.5 miles in more than than 4.5 hours of training. martha runs at a speed of 6 mph and bikes at a rate of 15.5 mph.