Homework Help: Magnetic fields

1. The problem statement, all variables and given/known data

An artery has an inside diameter of 3.20 mm and passes through a region where the magnetic field is 0.065 T.
If the voltage difference between the electrodes is 155 µV, what is the speed of the blood?

2. Relevant equations

V=kq/r E=kq/r^2 v=E/B

3. The attempt at a solution

I know that I have to ultimately use the last equation to find out velocity, but I need to first find out E. I tried using the second equation, but I am not quite sure as to what I'm doing wrong. First of all, is that right equation? For q, am I supposed to use the charge of an electron/proton? is r supposed to be entire diameter or should I divide it half?

 

In my calculations I wasn't able to include V, but I know that I should. However, I don't know how the two relate to each other in an equation....Also, I don't think that I've learned about emf...