Three long straight wires carrying current are arranged mutually...

The force per unit length between parallel wires is $F/L = \frac{\mu_0 I_1 I_2}{2\pi d}$.
Force on Q from P (opposite currents, repulsive towards R): $\frac{F_{QP}}{L} = \frac{4\pi \times 10^{-7} \times 3 \times 1}{2\pi \times 0.03} = 2 \times 10^{-5}$ N/m.
Force on Q from R (same currents, attractive towards R): $\frac{F_{QR}}{L} = \frac{4\pi \times 10^{-7} \times 1 \times 2}{2\pi \times 0.02} = 2 \times 10^{-5}$ N/m.
Total force per unit length towards R: $4 \times 10^{-5}$ N/m.
For 0.15 m length: $F = 4 \times 10^{-5} \times 0.15 = 6 \times 10^{-6}$ N towards R.