Question

find roots of this equation y^3-1.5y^2+0.3275

Answer 1

I see no equation

If you mean y^3 - 1.5y^2 + .3275 = 0
would rather work with integers, so multiply each term by 400
400y^3 - 600y^2 + 131 = 0

I don't know where you are at in your math studies.
Have you learned a way to solve cubics?
One way is to use Newton's Method, this requires knowledge of Calculus

I just ran your equation through Wolfram and got

http://www.wolframalpha.com/input/?i=400y%5E3+-+600y%5E2+%2B+131%3D0

Using the original, produced the same results
http://www.wolframalpha.com/input/?i=y%5E3-1.5y%5E2%2B0.3275%3D0