Is y=9-x proportional?

Write an equation in point-slope form for the line through the given point that has the given slope (-2,-7); m=-3/2

Solve 2x+y=3 x+y=5 in substitution method

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