Bevel gear $2$ is driven by the engine in the reduction unit illustrated in the Figure. Bevel planets $3$ mesh with crown gear $4$ and are pivoted on the spider $($arm$),$ which is connected to propeller shaft B$.$ Find the speed ratio between shaft A and B$.$ N$2=36$T$,$N$3=21$T$,$N$4=52$T; crown gear $4$ is fixed.

$($Ans$.0\mathrm{.}409)$