Two long parallel wires are 7.5 cm apart…

Step 1. The force on each metre. $\dfrac{F}{L} = \dfrac{2 \times 10^{-7}\ \text{T m/A} \times 18\ \text{A} \times 30\ \text{A}}{0.075\ \text{m}} = 1.44 \times 10^{-3}\ \text{N/m}$, that is $1.44$ mN on each metre. The currents are in the same direction, so the wires attract.

Step 2. The quiet line. Between the wires, the field of wire 1 points one way and the field of wire 2 points the other way. They cancel at a distance $x$ from wire 1 when $\dfrac{I_1}{x} = \dfrac{I_2}{d - x}$. So $x = \dfrac{I_1 d}{I_1 + I_2} = \dfrac{18 \times 7.5\ \text{cm}}{48} = 2.81$ cm.

Step 3. The $2.4$ m length. $F = 1.44\ \text{mN/m} \times 2.4\ \text{m} = 3.46$ mN.