If Reading win then Watford and Leeds cannot catch them and they will be promoted.
If Reading win and Sheffield United lose then Reading will be champions.
If Reading win and Sheffield United draw then Reading would be 18 points clear with only 18 more available. Reading would also have a goal difference of at least 33 better than the Blades, but even so would not be mathematically champions.
If Watford win, Reading have to win in order to go up. A draw for Reading would not be enough.
If Reading draw, they need Watford and either Leeds or Sheffield United to drop points. This is because Leeds face Sheffield United later in the season, so they could not both win all their remaining games.
Reading cannot draw and take the title.
If Reading lose, they require Watford to lose and in addition Sheffield United must lose or Leeds draw or lose.
Everyone got that clear? Good. You will be tested later! and just so long as Leeds win