SOLUTION: 5y-20=7x 20y=28x+40

Let me re-write your equations in this equivalent standard form:

 7x -  5y = -20,    (1)
28x - 20y = -40.    (2)


Now, I see that the second equation has the coefficients proportional to that of the first equation with 
the proportionality coefficient 4.

But the right sides are not in this proportion.


It means that the system IS NOT CONSISTENT. In other words, it has no solutions.