6*y^10-(3*y^6)+((8*y^4)/3y^2
You brackets are not quite right but I think that this is what you mean :)
$$\\6*y^{10}-(3*y^6)+((8*y^4)/(3y^2))\\\\
6y^{10}-3y^6+\frac{8y^4}{3y^2}\\\\
6y^{10}-3y^6+\frac{8y^2}{3}\\\\$$
This cannot be simplified any further.