The half tongue in cheek answer is that the range of a PA-28 is an unknown quantity, because
- nobody taught you how to lean the engine
- the fuel gauges are useless
- there is no fuel totaliser
- the tachometer is probably knackered so setting an accurate RPM, hoping to get the fuel flow in the manual, cannot be relied on
The only way is to find a way to lean for peak EGT, or some nearby operating point, in cruise. With no instrumentation, the way to do this is to set a power setting of say 65% (use the manual to find the RPM) and then lean until the power suddenly drops off, then advance the mixture back until the power is just restored.
Then do two identical flights which differ only in the length of the cruise segment. Top off before/after each flight, and then by subtracting the fuel usage on the two flights you get an accurate figure for the cruise fuel flow at that power setting. This will be specific to that aircraft.
Then, you can fly reasonable distances with some confidence.
Otherwise, the range is about 200 miles.