Water level after 25% on 90 Gallon
Assuming you have the 48x18x24 90Gal tank and an average of like 3" substrate. That leaves about 48x18x21 or 18411cu in or 78Gal water + a little in the substrate.
25% of that is 19.5Gal so you'd have 58.78 gal left in the tank + some in the substrate, which would take up about 13608cu in.
Your width and length don't change, so that looks like about 15.75" of water in the tank+ 3" substrate and assuming the black trim is about an inch and a half, 3.75" from the bottom of the black trim.
Please keep in mind there's a lot of guesstimates in this due to the substrate.