We need all rows to be equivalent, so try adding up the bottom (complete) row to get 7x-4x+3x=10x-4x=6x.
To solve the middle number, we have -2x+X+6x=6x, so X=2x. To solve the top number, we have X+8x-3x=6x, so X=6x-8x+3x=x
Now check first column, x-2x+7x=6x ok Second column 8x+2x-4x=6x ok Top-right to bottom-right diagonal: x+2x+3x=6x, ok Bottom-left to top right diagonal: 7x+2x-3x=6x
