Electrons through wire work physics problem

[tag16]

Homework Statement

Electrons move in a wire in the direction shown through an electrical device at the rate of 5*10^19 electrons per s. If the two ends of the device are at different electric potentials, V(a)-V(b)=-3 Volts, and if the electrons emerge at the same speed with which they entered, then the rate at which work is being done on the device is?

https://elearn.wmich.edu/webct/urw/lc571145591061.tp572778900061/RelativeResourceManager?contentID=572779805061

Homework Equations

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The Attempt at a Solution

I'm just not sure what the equation for work would be here, even though I probably already know it and can't remember but I didn't see it in my physics book either.

 

[rl.bhat]

Rate of doing work = power = V*I
Current = dQ/dt = n*e/dt.
N is given, e is known and dt = 1 s. Find W.