How much should I ask as a 24 hr/6day a week live-in nanny/tutor?

I've been offered a position for the summer as a live-in nanny. Part of my duties would include overseeing the older two girls lessons and finding ways to improve their English, both spoken and written. The hours would be all day/6 days a week. They will pay for my ticket to fly to France and summer there with them because they want a native English speaker. I've tried to research what the salary would be for this but most people just talk about a regular 40 hour work week. Anybody know what I should ask for? Thanks for the help!