In its first month of operations, Crane Company made three purchases of merchandise in the following sequence: $(1)350$ units at $$6,(2)400$ units at $$7,$ and $(3)250$ units at $$8.$

$($a$)$

Calculate the average unit cost. $($Round answer to $2$ decimal places, e$.$g$.15\mathrm{.}25.)$

Average unit cost

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