[tex]\huge\boxed{-5}[/tex]
The constant of proportionality can be found very easily in this example. Since [tex]x[/tex] and [tex]y[/tex] are directly proportionate, the constant of proportionality can be represented as [tex]r[/tex] in the following equation:
[tex]y=rx[/tex]
Since the equation in the problem is given to us in this format, we know that [tex]r=\boxed{-5}[/tex].
