Answer
-5 is the missing number, $m=-2$
Work Step by Step
If the value of x increases by 1 unit (from -1 to 0), the value of y decreases by 2 units.
Therefore the value of $y$ when $x$ is $1$ is $-3-2=-5$
m is the change in $y$ divided by the change in $x$.
Therefore $m=-2/1=-2$