Unsure how much to charge.

Hi everyone! I hope this is okay to ask as i really need some advice. A client is having me watch their dog 10 hours straight. They dont want me to leave other than short trips for food. I know i need to charge a higher rate since I cant leave but im not sure whats too much or too little to ask for. I have my drop in rate set $16/30 minutes, it may be a little low. I know it depends on several factors but based only on what ive said so far, what would you ask for?