What is the formula for the nth of the sequence 6, 9, 12, 15, 18

Step-by-step explanation:

$21

Let the amount Lori bought the shirt and the hat be $x, if she bought them at half off sale, the initial price of both item will be 2 × $x

If she spent $21 on both items, the initial price will have been 2 x $21 = $42 where x is $21

Original price of the hat and shirt is therefore $42. Since both are on half off sale, the initial price is the hat will be $42/2 = $21