that line could have an infinite possibilities of height, for example if the tank is cubic, 20 inches per side, then we can calculate the line's height:
volume = 2020height
given the fact that the tank has 20 inches per side, and we know the volume as a data given:
1050 = 2020heigth
hence the height is:
height = 1050/400
height = 2.63 inches