Volume of water in container 1 is 5*4*10=200cc. If h is the height of the water in both containers after transfer, then, if the base of container 1 is 5 by 4, then the volume of water in container 2 is 6*5h=30h. The level of water in container 1 drops by x cm, therefore 30h=20x and x=3h/2. The height of the water remaining in container 1=10-x=10-3h/2. But this is the same height as the water in container 2, so 10-3h/2=h, and 5h/2=10, making h=4 cm.
The volume of water in container 1 is 5*4*4=80cc and the volume of water in container 2 is 30h=120cc. The total amount of water is 80+120=200cc, the volume of container 1.