What are the units of 4*2 sheets ?
My approach was 1 million liter cube implies each side is 100.
Therefore area of each side 10000. No of sheets required would be 10000/(4*2) = 125 (but this no where close) since units of 4*2 sheets are not specified.
So if I have to make a guess it would be 12 since that is the only one which is multiple of 6 (6 surfaces)