What is 9 over 10 as an decimal

Anyone know? will mark brainliest if correct!

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

For the inequality |c| < |d| to be true, which of the following must be true?