
Answer:
a) Â B = 0.9375 T Â -z, b) Â Â Â B = 1.54 T
Explication
a) The magnetic force is
     F = q v x B
     f = q v B sin θ
bold indicates vectors
For direction let's use the right hand rule.
If the charge is positive
the flea in the direction of velocity, toward + x
the fingers extended in the direction of B
the palm the direction of the force + and
therefore the magnetic field goes in the direction of -z
      F = q v B
      2.25 10-16 = 1.6 10-19  1.50 103 B
      B = 2.25 10-16 / 2.4 10-16
      B = 0.9375 T  -z
b) now an electron
thumb speed direction, -z
opposite side of palm force + y
therefore the direction of the magnetic field is + x
      B = F / qv
      B = 8.5 10-16 / 1.16 10-19 4.75 103
       B = 1.54 T