An electric current I $=0\mathrm{.}55$ A is moving in a circular wire with radius R $=0\mathrm{.}075$ m$.($a$)$ express the magnetic field vector B generated at the center O in terms of the current I, the radius vector R$,$ and the length element vector ds$.($b$)$ What's the direction of the magnetic field at point O$?($c$)$ Express the magnitude of the magnetic field at point O in terms of I and R$.($d$)$ Calculate the numerical value of B$,$ in telsa.