Per kg charge in check in

Hi, I’m traveling from Seattle to India via Dubai in Economy class and wanted to purchase extra kilograms for my checked luggage. However, I could only find the option to buy an additional bag online. When I called the airline, they mentioned that extra weight would be charged at the airport, but they couldn’t provide details about the charges.

I was wondering if anyone who has traveled this route could share their experience regarding the cost of extra weight at the airport. Additionally, are the staff at Seattle strict about carry-on luggage? Do they weigh it, and is a laptop bag considered a separate personal item?

Thanks in advance!