Final answer:
To find the total amount Katie must pay for the dress, add the original price of the dress and the sales tax. The total amount Katie must pay for the dress is $42.40.
Step-by-step explanation:
To find the total amount Katie must pay for the dress, we need to add the original price of the dress and the sales tax. The sales tax is 6%, which means Katie needs to pay an additional 6% of the original price. To calculate the sales tax, multiply the original price ($40.00) by 0.06. The sales tax is $2.40. Now, add the original price and the sales tax: $40.00 + $2.40 = $42.40. Therefore, the total amount Katie must pay for the dress is $42.40.