a full tank should make u be able to drive +-100km but this depends on your camino (what state he is in and what setup u use) but it also depends on your driving style if u accelerate much ( i mean giving gas then loosen gas and giving gas againe ) then u will use up more feul then if u would drive at constant speeds
but still it should be somewhere around the 100km

you don't have a km-counter, than you can easy see or calculate it

I did 120 km with a full tank back in the days when I went to school. Engine was untouched 50cc.

i do 110km with a full tank mine's a 60cc k-star
for the rest untouched, if you have to drive slow you can better drive on a slower constant speed
than giving gas and loose it