What is the Correct Way to Calculate the Work Function of a Material?

[Centaginous]

Homework Statement

When a monochromatic light with a wavelength of 254 nm falls onto the surface of a particular metal it causes a photocurrent to flow. A stopping voltage of 2.30 V is required to completely block the photocurrent. What is the work function of the material?

Homework Equations

KE = hf - W_o
hf = hc/wavelength

The Attempt at a Solution

I keep getting a negative number which is an impossible answer for a work function.
Any help would be greatly appreciated.

Thank you.

 

[rl.bhat]

Before solving convert stopping potential to energy units.(J)
Show your calculations.

 

[Centaginous]

Thanks for pointing that out. I had the wrong units which messed up everything.