Remember

Volume of a cuboid= length × breadth × height

1 cm=1 ml

1000 ml=1 liter

Volume of a cuboid= 20 x 20 x 20 = 8000 cubic cm

then

1 cm=1 ml

so

8000 cubic cm = 8000 ml

and

1000 ml=1 liter

so

8000 ml = 8 liter