Does anyone know the answers to this?

What is the inverse of the function f(x) = 2x + 1?

One integer is 8 times another. if the product is 72, then find the integers

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