How would you separate water from antifreeze?

Not a chance, you could only remove sediment. The ethylene glycol is in solution.

For recycling antifreeze (at the higher concentrations normally used), the solution is first highly filtered & then partially fractionally distilled (ethylene glycol has a boiling point 196-198°C, so the excess water can be boiled off). This would take an enormous amount of energy in your case, however.

For trace amounts, a chemical or electrochemical oxidation oxidation method could be used to destroy the molecule all the way to H2O & CO2.  You could consider ozone, electrocoagulation, etc., which will get rid of other impurities as well.

Probably, your most economical solution is ultrafiltration or RO.

How do we find the answer?

A1 a 2 a 3 ooh lol i think that's it