Assume that the process starts empty, that set$-$ups at steps B and C can not begin until work arrives, that the production batch is $10$ units at each step, and that the transfer batch between steps $1$ and $2,$ and between steps $2$ and $3$ is also $10$ units $($i$.$e$.,$ the units in a production batch must be moved together between steps.$)$ How long does it take to complete a batch of $10$ units?

Assume that the process starts empty, that set$-$ups at steps B and C can not begin until work arrives, that the production batch is $10$ units at each step, and that the transfer batch between steps $1$ and $2,$ and between steps $2$ and $3$ is also $10$ units $($i$.$e$.,$ the units in a production batch must be moved together between steps.$)$ How long does it take to complete a batch of $10$ units?

$250$ minutes

$278$ minutes

$320$ minutes

$375$ minutes

$420$ minutes