Question

what is the answer to 2y-8x=20

Answer 1

Pick a number.  Any number.  Call it 'x'.

Multiply 'x' by  4.
Add  10  to the product.
Call the current number  'y'.

The 'x' and 'y' that you have now are an 'answer' to that equation.

Do it as many times as you like.  There are an infinite number of them.

Answer 2

        2y - 8x = 20
2y - 8x + 8x = 20 + 8x
               2y = 20 + 8x
                2          2
                 y = 10 + 4x