LOL HELP I literally forgot how to do basic maths

Nine more than four times a number is the same as one less than twice the number. find the number?

The clayton family’s pool has vertices at the coordinates (0, 2), (0, 5), (2, 5), (2, 6), (5, 6), (5, 1), (2, 1), and (2, 2). if each grid square has an area of 9 square feet, what is the area of the pool?

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