Can someone me and break this down for me. i don’t get number 16

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

What is the slope of the line shown below?

What is the value of x in the equation7x+2y=48 when y=3