I have the m1=1139, v10=1.984,and vf=1022 but I need to find m2 and I don't know how I'm supposed to do that. The equation m1*v10=(m1+m2)*vf. Please help as soon as you can.

An investigator needs a uniform 30 mt field, which she intends to produce with a solenoid. she takes a long 10-cm-diameter tube and wraps wire along the length of it, wrapping 1200 turns of wire along a 75-cm length of the tube. how much current must she pass through the wire to produce the desired field?