At a certain store the taco sauce was on sale for 1/5 off. with a coupon for an additional 40 cents off, the final cost of the sauce was $1.20

Jada has a meal in a restaurant she adds up the prices listed on the menu for everything they ordered and gets a subtotal of $42.00. when the check comes, it says they also need to pay $3.99 in sales tax. what percentage of the subtotal is the sales tax