given

x-200=3/7y...we have to calculate y

stmt 1:x=1/2y....sufficient

stmt2:
y-1600=3/7y..sufficient

stubbornp wrote:given

x-200=3/7y...we have to calculate y

stmt 1:x=1/2y....sufficient

stmt2:
y-1600=3/7y..sufficient

Statement 2 how ever does not say how full the tank was when 200 liters was removed.
i.e the problem never says if the 200 liters were acutally removed when the tank was quater full or half full ..

In this case we don't need to know how much the tank was filled before the 200 gallons were removed because due to statement 2 we know:
the amount left in the tank (3/7's of a tank)
and the coincidental 4/7's that is not there (1600 gallons)

From those numbers we can get the amount of oil left.

IMO D as well.

assume C to be the tank capacity & V to be the volume of oil in it...

From the question we can infer that V-200=3/7C

From statement 1: V=1/2C

1/C-200=3/7C .....hence capacity can be determined

From statement 2: V-200=C-1600

C-1600=3/7C....hence capacity can be determined

So the ans is D..