Answer:

Explanation:
Force on a current carrying rod due to magnetic field is given as

here we know that
current in the rod


now magnetic force is balanced by the weight of the rod
so we will have



I got B,when you subtract 3/5 from NEGATIVE 2/3 it creates a negative 19 over a positive 15.
1 is 0n I believe 2 8n or 2n 3 would be 10n 4 is 0n or 12n