sqrt(18x^5y) + sqrt(32xy^3) - sqrt(128xy)
You may separate the roots to produce solvable square roots!
sqrt(9x^4)*sqrt(2xy) + sqrt(16y^2)*sqrt(2xy) - sqrt(64)*sqrt(2xy)
Simplifying makes it ...
(3x^2 + 4y - 8)*sqrt(2xy)
This should be the closest you can get to a simplified equation.