Question

I don't understand this.

Answer 1

3x + y = 6.  You're free to choose any x values you wish (at least, for this linear function).  So, if you chose x = 0, y would be 6, and you'd enter    0      6    in the first row of the given table.

If you chose x = -2, then -6 + y = 6 and y would be 12.  Enter        -2     12  in the second row of the table.

You could also choose y values and calculate the related x-values.