HELP Write the standard form of an equation

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?

Neal buys a board game. he pays for the board game and pays $1.54 in sales tax. the sales tax rate is 5.5%. what is the original price of the board game, before tax

Luisa sells stuffed animals. she sells her stuffed elephant for $34.90, and the sales tax is 6% of the sale price. about how much is the sales tax on the elephant?