Elaines car showed that her gas tanks was 6/8 full her car can hold 12 gallons how many gallons were there when she look at the gas guage?

You have to find an equivalent denominator.  The two fractions are 1/12 and 6/8. I'll show you some work.

6/8 ; 12/16 ; 18/24

1/12 ; 2/24

Now that we know the denominator is 24, we can simplify 18/24.

18/24 ; 9/12

Your answer should be 9/12. Hope this helps! :)