Whatwhat are the coordonates of the point that is 3/8 of the way rom A(-8,-9) to b(24,-1)

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