Magnetic Field of Straight Wires question from NEET 2015 (AIPMT, Cancelled Paper)

Answer: (a)

1. Each semi-infinite wire along X at distance $R$ from O: $\frac{\mu_0 I}{4\pi R}$; by $I\,d\vec{l} \times \hat{r}$ both point along $-\hat{k}$.
2. Wires together: $-\frac{\mu_0 I}{4\pi R}(2\hat{k})$.
3. Semicircle in Y-Z plane: $\frac{\mu_0 I}{4R} = \frac{\mu_0 I}{4\pi R}\pi$, directed along $-\hat{i}$ for the current shown.
4. $\vec{B} = -\frac{\mu_0 I}{4\pi R}(\pi\hat{i} + 2\hat{k})$
5. So the answer is (a).