Explanation

(c) Force on wire $C$ due to wire $D.$
$F_{1} = \frac{\mu_{0}}{2\pi}\frac{I_{1}I_{2}}{r}l$ (repulsive)
$\ \ \ \ \ = 2 \times 10^{- 7} \times \frac{30 \times 10}{3 \times 10^{- 2}} \times 25 \times 10^{- 2}$
$\ \ \ \ \ = 2 \times 10^{- 7} \times 2500 = 5 \times 10^{- 4}\ N$
Force on wire $C$ due to wire $G$
$F_{2} = \frac{\mu_{0}}{2\pi}\frac{I_{1}I_{2}}{r}\ l$ (repulsive)
$\ \ \ \ \ = \frac{2 \times 10^{- 7} \times 10 \times 20}{2 \times 10^{- 2}} \times 25 \times 10^{- 2}$
$\ \ \ \ \ = 2 \times 10^{- 7} \times 2500 = 5 \times 10^{- 4}\ N$
Net force $= F_{1} - F_{2} = 5 \times 10^{- 4}\ N - 5 \times 10^{- 4}\ N = 0$