So after that 180 mile ride, my bike took 13 1/2 litres as an absolute max I could fit in there. On google it says the tank holds 16 litres, which is 3.5 imperial gallons.
Since mine used 13 1/2 in 180 miles (I fully brimmed it before the long ride), that makes 2.969 gallons, just call it 3 gallons used.
180 divided by 3 is 60. Colour me massively impressed at that!

Note I am in the UK, so I assume in the US you use US gallons which would change the result.
Either way thats almost double what my car can do.

Edit: Also note I recently did the following:

Brand new tyres
Coolant change
Braided brake line and fluid change
Cleaned out the brake drum and correctly set the lever
Spark plug change
Oil and filter change
Fork oil change
New air filter

Riding 1 up, fairly large screen and lowers.

You used 3.603 us gallons, for an average fuel economy of 49.95mpg. About average for a C50 ridden at moderate speeds. You had .485 gallons remaining in reserve, which would give you a maximum theoretical range of 200 miles. Of course, fuel economy will vary, so do not take one tank to mean you will always see such performance. Ride it a little faster or fill it just slightly less and you'll be pushing the bike.