Two identical circular loops P and Q each of radius r are lying in parallel planes such that they have common axis. The current through P and Q are I…

Two identical circular loops $\displaystyle P$ and $\displaystyle Q$ each of radius $\displaystyle r$ are lying in parallel planes such that they have common axis. The current through $\displaystyle P$ and $\displaystyle Q$ are $\displaystyle I$ and $\displaystyle 4 I$ respectively in clockwise direction as seen from $\displaystyle O$. The net magnetic field at $\displaystyle O$ is: