The answer is 1.
To find the answer you would take y/ x for the first thing in the table ( -2/1 ) then the second row of the table ( -1/2 ) then you would find out how much the points increased or decreased.
In this case y went up 1 and so did x so the slope would be 1/1 or just 1. Then check with the other points to make sure it is linear throughout then bam done. :)