An 11Ah battery has 396 Watt/hours, at 36v. You can reckon on 10-20 watt/hours per mile. Giving you a range of approx. 20 - 40 miles. Bit vague I know, but there's so many variants. Hills (not many for you) wind (ooer yes) weight, amount of rider effort, temperature etc.
I have a rack...