A current of 30 A each flows in opposite directions in two...

Let the distance between the wires be $d = 8\text{ cm}$. The distance of the midpoint from each wire is $r = \dfrac{d}{2} = 4\text{ cm} = 0.04\text{ m}$.

The current in each wire is $I = 30\text{ A}$.

Since the currents flow in opposite directions, the magnetic fields produced by both wires at the midpoint point in the same direction and add up.

The total magnetic field at the midpoint is:

$B_{\text{net}} = B_1 + B_2 = \dfrac{\mu_0 I}{2\pi r} + \dfrac{\mu_0 I}{2\pi r} = \dfrac{\mu_0 I}{\pi r}$

Substituting the given values:

$B_{\text{net}} = \dfrac{4\pi \times 10^{-7} \times 30}{\pi \times 0.04}$

$B_{\text{net}} = \dfrac{120 \times 10^{-7}}{0.04}$

$B_{\text{net}} = 3000 \times 10^{-7}\text{ T}$

$B_{\text{net}} = 300 \times 10^{-6}\text{ T} = 300\ \mu\text{T}$

Answer: $300$