Moving Charges And Magnetism

Two long parallel wires carry currents $I_1$ and $\mathrm{I}_2\left(\mathrm{I}_1>\mathrm{I}_2\right)$. When currents are flowing in the same direction, the magnetic field at a point midway between the wires is $6 \times 10^{-6} \mathrm{~T}$. If the direction of $\mathrm{I}_2$ is reversed the field at midpoint becomes $3 \times 10^{-5} \mathrm{~T}$. The ratio $\mathrm{I}_1: \mathrm{I}_2$ is