Two parallel wires carry currents in the same direction. I$1=3$A and $I_2=1$A and the distance between the conductors is $4$ cm $.$ The magnetic field midway between these two wires is:

a$)4{10}^{-5}T$

b$)0$ T

C$)2{10}^{-5}T$

d$)3{10}^{-5}T$