into two cells every $20$ minutes. The initial population of a culture is $40$ cells.

$($a$)$ Find the relative growth rate.

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$($b$)$ Find an expression for the number of cells after $\backslash ($ t $\backslash )$ hours.

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$($c$)$ Find the number of cells after $4$ hours.

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$($d$)$ Find the rate of growth after $4$ hours. $($Round your answer to the nearest integer.$)$ cells$/$h

$($e$)$ When will the population reach a million cells? $($Round your answer to two decimal places.$)$

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