The magnetic field at C due to first conductor is
B1 =
(since, point C is separated by d +
=
from 1st conductor). The direction of field is perpendicular to the plane of paper and directed outwards.
The magnetic field at C due to second conductor is
B2 =
(since, point C is separated by
from 2nd conductor)
The direction of field is perpendicular to the plane of paper and directed inwards. Since, direction of
B1 and
B2 at point C is in opposite direction and the magnetic field at C is zero, therefore,
B1 =
B2 =
On solving I = 30.0 A