Resoluçao:

N(t) = 9 . 3 ^4t/300 

27 = 9 . 3 ^4t/300 

3³ = 3² . 3 ^4t/300 

^{4t/300 = 1}

^{4t = 300}

^{t = 300/4}

^{t = 75 dias}

Resposta: 75 dias.