Let function $F : A\rightarrow A$ satisfying :- \[ 2F(x) + F(\frac{x}{x-1})= \frac{5x^2-x}{2x^2+x-1}\] where $x$ is an element of the set $A$ . If $A$ is a proper subset of the set of real numbers , find the sum of all possible values of $F(51)$ .