Physics education research, electronic materials, and the musings of Christopher Moore, Ph.D.

I am working on AP problem 1993B3, but I am having a really hard time. the problem is:
A particle of mass m and charge q is accelerated from rest in the plane of the page through a potential difference V between two parallel plates.  the particle is injected through a hole in the right-hand plates into a region of space containing a uniform magnetic field of magnitude B oriented perpendicular to the plane of the page. the particle curves in a semicircular path and strikes a detector.
A. I) State whether the sign of the charge on the particle is + or -
   II) State whether the direction of the magnetic field is into the page or out

B. Determine the following in terms of m, q, V, and B
    I) the speed of the charged particle as it enters the region of field B
   II) the force exerted on the charged particle by field B
  III) the distance from the point of injection to the detector
   IV) the work done by the field on the charged particle during the semicircular trip

Here is where I have gotten:
A. I) the charge would have to be positive (i used the right hand rule)
    II) out of the page (right hand rule again)
B. I) I have tried a bunch of different things such as setting qvB = (mv^2)/r (which i now know is not right), using the B= uknot/2 X I/r and setting it equal to all sorts of things...I am totally confused and have no idea what to try next...
   II) I think that you would use F=qVB and just plug in your answer from above into V and solve, right?
  III)here is what i tried if you can follow it
B=(uknot/2)(I/r) -> B=2pi (I/r) -> I=P/v so B=2pi (p/vr) -> p=mv so B= 2pi (m/r) so r = (2pi m)/B and then that times 2 since the distance would be 2r.
IV) w= qEd maybe? I have no idea