So you need to find the volume of the rectangular prism and the equation for that is V=l×w×h. If you plug those numbers in you'd get 9×12×23=2,484. If you multiply 2,484 by \(\frac{1}{3}\) because you'd have to pour out \(\frac{1}{3}\) of the water out so that it's only \(\frac{2}{3}\) of the volume of water is left. 2,484×\(\frac{1}{3}\)= 828mm.