Given a linear equation [tex]\displaystyle{y=mx[/tex], the constant of proportionality is
[tex]\displaystyle{m[/tex], which is [tex]\displaystyle{\frac{y}{x} [/tex].
Thus, the constant of proportionality of [tex]\displaystyle{y=4x[/tex] is [tex]\displaystyle{\frac{y}{x} [/tex] which is 4.
Answer: 4
