You are still doing it wrong, sorry. You mentioned, yet again, decimal places, and that is not how scientific notation works. Here's a little trick you can try, that might help you to understand: convert all numbers in your problem to exponential notation, then you will see how many decimal places, which you seem to be hung up on, they really have. Maybe the instructor is trying to get you to do this, since the answer is in exponential format. Sadly, spreadsheets like EXCEL do round by decimal places without regard to actual significant figures, so it can get hard you new students to think about significant figures correctly, if they've experienced rounding on computers first.