In Fig. $29-77$, a closed loop carries current $i=200 \mathrm{~m} \mathrm{~A} .$ The loop consists of two radial straight wires and two concentric circular arcs of radii $2.00 \mathrm{~m}$ and $4.00 \mathrm{~m}$. The angle $\theta$ is $\pi / 4 \mathrm{rad}$. What are the (a) magnitude and (b) direction (into or out of the page) of the net magnetic field at the center of curvature $P ?$