Answer:
57.5
Explanation:
The constant of proportionality is "k" in the equation ...
y = kx
It can be found from values of x and y using ...
k = y/x
For the given values, it is ...
k = (287.5 mi)/(5 h) = 57.5 mi/h
The constant of proportionality relating miles to hours is 57.5.