Why such extremely low gas mileage per gallon?

MATH? are you kidding me with that answer? And you call yourself a Master.. LOL! BELIEVE me when I say we are only getting 7, at most 10 mpg, and that's no bull. I know my math very well. This vehicle has a 13.5 gal. tank. At less than 1/2 full when we started out, we put on 65 miles round trip today, and returned with a nearly empty tank.. ok, now YOU figure it out! This is a serious question, not a joke and I'm looking for a serious answer. Thanks anyway, but this isn't a laughing matter.

Master?... Just been fixing em for 40 years so,.....,Fill tank till pump nozzle cuts off first time!!.. Drive say..100 miles.. Fill tank again, same way... How many gallons???? Then YOU do the math!!.. You see it's YOUR mpg to figure out, not mine!!!.. Besides, if it were actually 'burning' that much gas, the exhaust would have 'black' smoke, 4 CYLINDER ENGINE would be running like s--t... check engine light on with multiple codes!!..SERIOUSLY!!!!! Cheers..