A hobby store prices model train track using a proportional relationship between the length of track (in inches) and the cost in dollars. If 6.4 inches of track costs $16, what is the constant of proportionality?

Melanie is buying a bathing suit that costs 39.99. she is given a discount at the cash register of $6.00 when she scratched 15% off on a game piece for a store promotion. what will the sale price of melanie’s bathing suit be?