Demand for rug$-$cleaning machines at Clyde$$s U$-$Rent$-$It is shown in the following table. Machines are rented by the day only. Profit on the rug cleaners is $$20$ per day. Clyde has $3$ of the rug$-$cleaning machines.

Demand Frequency

$0\mathrm{.}30$

$1\mathrm{.}20$

$2\mathrm{.}20$

$3\mathrm{.}15$

$4\mathrm{.}10$

$5\mathrm{.}05$

$1\mathrm{.}00$

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a$.$ Assuming that Clyde$$s stocking decision is optimal, what is the implied range of excess cost per machine?