Chemistry help (density)?

[jules]

Problem: You are given a piece of plastic that you know has a density of 0.90 g/mL. But I don't have a balance to prove it. I have to design en experiment to prove that the density of the plastic object if 0.90 g/mL. I am given two solutions:

Density of water= 1.00 g/mL
Density of alcohol solution= 0.85 g/ml
^How an I use these two substances to show that the density of the plastic is around 0.90 g/mL

I know that I can experiment it by using water replacement but that was an option I can not do b/c at the end I would have to compare water replacement and my own experiment. Can you give me any ideas how to come up with an experiment?
Thank you very muh.