Question: If a concrete class extends an abstract class which implements an interface in java is it possible to overload any of the methods from the interface more in the concrete class?

Answer: 
If you're too lazy to do the algebra:

[Wolfram Alpha says](http://www.wolframalpha.com/input/?i=Solve%7Bx+%2B+y+-+x*y+%3D%3D+c1%2C+x+%2B+z+-+x*z+%3D%3D+c2%2C+a*y+%2B+b*z+%3D+c3%2Cx%2Cy%2Cz%7D) in the most general case (assuming none of these denominators are zero):

```
x=(a*c1+b*c2-c3)/(a+b-c3)
y=(b*c1-b*c2-c1*c3+c3)/(-a*c1+a-b*c2+b)
z=(a*(c1-c2)+(c2-1)*c3)/(a*(c1-1)+b*(c2-1))

```
I'd recommend `rSymPy`, the R port of the awesome python library for symbolic math.

```
library(rSymPy)
sympy("var('x,y,a,b,z,c1,c2,c3')") # declare vars
sympy("solve([Eq(x+y-x*y,c1),Eq(x+z-x*z,c2),Eq(a*y-b*z,c3)],[x,y,z])",
      retclass="Sym")

```