problem $12$:

Determine the Shaft diameter for each of the following figures, given that: $N=600rpm,$

${}_{\text{a}\text{l}\text{l}}=40$MPa. $($The ratio of the belt tensions is $3$:$1-Kb=Kt=1\mathrm{.}5-$ Dimensions in mm $.)$

Assume any missing data. $($ i need solution step by step $)$