If in the figure, $($W$/$L$)18=100/0\mathrm{.}5$ and ISS $=1$ mA$,$

$($a$)$ What CM level must be established at the drains of M$3$ and M$4$ so that ID$5=$ ID$6=1$ mA$?$ How does this constrain the maximum input CM level?

$($b$)$ With the choice made in part $($a$),$ calculate the overall voltage gain and the maximum output swing.