Hmm son I think you need a system of equations with x and y variables to solve that aka: ax+by=c and dx+ey=f with a,b,d,e the coefficients and c,f the constants. As for your question i think you want to state that 2x+5y=10 but without another branch its unsolvable, well as for real numbers goes you can always put the x form one side and solve for it aka:
2x+5y=10<=>2x=10-5y<=> x=[10-5y]/2
