Anyone help he due in 30

15 points ! ~ see if you know the answer to both you!

The angle of a triangle are given as 6x,(x-3), and (3x+7). find x then find the measures of the angles

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