A body having moment of inertia of $30$ kg m$2$ is rotating at $210$ RPM and meshes with another body at rest having M$.$I. of $40$ kg m$2.$ The resultant speed after meshing will be

A$\mathrm{.}90$ RPM

B$\mathrm{.}100$ RPM

C$\mathrm{.}80$ RPM

D$.$Data are insufficient