Uncertainty for a particle diffracted through a single slit

[GMarks]

Homework Statement

A horizontal beam of laser light of wavelength 486 nm passes through a narrow slit that has width 0.0590 mm . The intensity of the light is measured on a vertical screen that is 2.90 m from the slit.
What is the minimum uncertainty in the vertical component of the momentum of each photon in the beam after the photon has passed through the slit?

Homework Equations

ΔyΔP_y ≥ h

The Attempt at a Solution

I tried simply substituting the slit width for Δy and solving for momentum, but that gave me the wrong answer. I'm extremely confused, as this shouldn't be a hard question but I can't seem to get an answer the system will accept. Can anyone help?

 

[haruspex]

ΔyΔPy ≥ h

You mean $\hbar$, right?
Please post your working and, if you know it, the official answer.