What weight of water is displaced by a 100-ton floating ship?
The answer must be in SI units. This part is driving me insane, because no matter how much I search for its possible solution, I can't find it.

A floating object displaces its own weight.  All you have to do is convert 100 tons to an SI unit of weight (force).1 ton = 2,000 pounds100 tons = 200,000 poundsThe SI unit of force (weight) is the Newton.  On Earth, 1 kg of mass weighs 9.8 newtons, or 2.205 pounds.(200,000 pounds) x (9.8 newtons / 2.205 pounds) = 888,900 newtons (rounded)