Answer: 5/4 or 1.25
The given equation y = (5/4)x is in the form y = kx
The constant of proportionality is the value of k, so k = 5/4.
If your teacher wants it in decimal form, then 5/4 = 1.25
Side note: the equation y = kx only applies to direct proportion equations. Inverse proportion equations will be in the form y = k/x.