An assembly line is to produce $420$ items in a standard $8$ hour day. What is the appropriate takt$$ time?

A$.$

$52\mathrm{.}50$units$/$minute$.$

B$.$

$137\mathrm{.}14$units$/$hour$.$

C$.$

$68\mathrm{.}57$seconds$/$unit$.$

D$.$

Cannot be determined without knowing what the activity times are.