cindy - it appears from your post that you have arriving in Venice covered and are asking about getting from your hotel in Venice to Marco Polo airport for a 9:40 am flight.
The time is not a problem, you can actually make it to Marco polo by 5:30 am using public transport.
You have two methods and each method has two choices. I'll try to outline them.
Water.
Alilaguna is basically a boat airport shuttle. There are several lines or routes and each departs from specific locations within Venice. Here is their website:
www.alilaguna.it
Current cost is 13 euros and that includes your luggage.
It takes about an hour and the boat drops you at the docks at the airport. then about a 10 minute walk to the terminal. you can buy tickets in advance or before you board. To get on Alilaguna, you'll need to get from your hotel to the arrival/departure point, probably by walking.
A private water taxi or motoscafi.
Very slick, very nice, pricey, but you'll feel like James Bond and maybe wish you had his expense account. Current pricing is around 100 euros from Venice to Marco Polo. If your hotel has a dock, they will pick you up there, if not they will pick you up at the closet place the speedboat can get to and you can get into to boat. You will arrange this method before hand and probably ask your hotel to set it up for you.
Land:
All land transportation leaves from Piazzale Roma. You will need to get from your hotel to P. le Roma. Depending on where you stay this may include walking, taking a vaporetto or both.
Once you arrive a P. le Roma, there are two buses that service the airport. One is a private company called ATVO. They run a large blue bus with big letteres that say ATVO on it. Hard to miss.
www.atvo.it.
cost for the ATVO bus is 3 euros.
The other bus is a big orange bus operated by ACTV, the same folks that run the vaporetto. I think the cost is 2 euros.
Buses take 20-25 minutes and drop you in front of the terminal.