The magnetic field at O

Question

$\begin{array}{1 1} \large\frac{\mu_0 I}{R} \bigg[\large\frac{1}{2 \pi} -\frac{1}{4}\bigg] \\ \large\frac{\mu_0 I}{R} \bigg[\large\frac{1}{2 \pi} + \frac{1}{4}\bigg]\\\large\frac{\mu_0 I}{R} \bigg[\large\frac{1}{4 \pi} -\frac{1}{4}\bigg]\\ \large\frac{\mu_0 I}{R} \bigg[\large\frac{1}{4 \pi}+\frac{1}{4}\bigg]\end{array} $