A company is preparing a bid on a government contract for $40$ units of a certain product. The operations manager estimates the assembly time required for the first two units to be $10\mathrm{.}4$ hours and $8\mathrm{.}8$ hours.

What is the average time per unit for the first $30$ units?

Multiple Choice

$3\mathrm{.}6$ hours

$4\mathrm{.}5$ hours

$5\mathrm{.}9$ hours

$4\mathrm{.}7$ hours

$5\mathrm{.}6$ hours