A rectangular coil of sides $12$ cm and $8$ cm is rotated in a magnetic field of flux density $1\mathrm{.}5$ T$,$ the longer side of the coil actually cutting this flux. The coil is made up of $94$ turns and rotates at $1300$ rev$/$min$.$ Answer the following a$)$ The maximum generated e$.$m$.$f$.$ and b$)$ If the coil generates $138$ V$,$ the speed with which it will rotate $=$