A beaker contains 100 milligrams of a solution of salt and water that is x% salt by weight such that $x < 90$. If the water evaporates at a rate of $y$ milligrams per hour, how many hours will it take for the concentration of salt to reach $(x + 10)$%, in terms of $x$ and $y$?

(A) $x^x y^y=\frac{24^3}{2}$

(B) $\frac{1000 + 99x}{xy+10y}$

(C) $\frac{100y+100xy}{x+10}$

(D) $\frac{1000}{xy+10y}$

(E) $\frac{\sqrt{x+y}}{2}$