Answer:
1/3 x 12
Explanation:
just find the time taken and the expression will just reveal itself
if 1/12 tank= 1/3 hrs
1 tank = 1 x 1/3
1/12
=1/3 / 1/12
=1/3 x 12
( not compulsory just thought some one might not wanna calculate but just know the time taken: )
1/3 x 12
= 4hrs)