Answer
The missing number is $-2.5$
$m=-\frac{1}{2}$
Work Step by Step
If the value of x increases by 2 unit (from 2 to 4), the value of y decreases by 1 units.
Therefore the value of $y$ when $x$ is $5$ is $-2-(1/2)=-2.5$ (Because from 4 to 5 $x$ only increased 1 unit)
m is the change in $y$ divided by the change in $x$.
Therefore $m=-1/2=-\frac{1}{2}$
