Determine which delivery alternative would be most economical for $80$ boxes of parts. Each box costs $$230$ and annual holding cost is $30$ percent of cost$.$ Assume $365$ days per year. Freight costs are:

Alternative Freight Cost $($for all $80$ boxes$)$

Overnight $$345$

Two$-$day $299$

Six$-$day $207$

Alternative

$($Click to select$)$

b$.$ For what range of unit cost for a box would each delivery alternative be least costly$?($Do not round intermediate calculations. Round the final answers to $2$ decimal places.$)$

Overnight is cheapest if unit cost $>$ $

$.$

Two$-$day delivery is cheapest if $

$<$ unit cost $<$ $

$.$

Six$-$day delivery is cheapest if unit cost $<$ $

$.$