A reverted gear train as shown in fig. $($a$)$ is used to provide a

speed ratio of $10.$ The module of the gears$1$ and $2$ is $3\mathrm{.}2$ mm

and of gears $3$ and $4$ is $2$ mm$.$ Determine the suitable number

of teeth for each gear. No gear is to have less than $20$ teeth. The center distance between shafts is $160$ mm$.$