What is your standard rate per hour? What is your mode of cutting.......pusher, ZTR, belly mount?? How many obstacles are you facing on this lawn and are there hills?
After you have done a few different lawns and learn the time needed for each, then you can factor in your hourly-base rate for a particular lawn..
In Arkansas you do not have to charge tax on mowing unless you are selling a product with it and of course, unless you are doing commercial and industrial properties.