Hello, I just have one question with three short parts, I was hoping I could recieve some help. I'd appreciate it, thanks. :)

Present population =PP
Future population   =FP

FP = PP x [1 + R]^N
FP = 400 x [1 + 1.5]^10
FP = 3,814,697 - populations of weevils after 10 weeks.
1,000,000 =400 x 2.5^N
2,500 = 2.5^N
N =log(2,500) / log(2.5)
N = 8.54 - Number of weeks when the population hits 1,000,000.

1.  A possible formula is

P = 400(2.5)^(N )     where P is the population after N weeks

[ Note  150%  actually means that the population increases by 2.5 times every week ]

2.  After 10 weeks we have

P  = 400(2.5)^ (10)  =  400 (2.5)^10  ≈ 3,814,697

3.  We need to solve this

1,000,000,000  = 400 (2.5)^(N)     divide both sides by 400

2,500,000 = (2,5)^(N )         take the log of both sides

log 2500000 = log 2.5^(N )      and by a log property we can write

log 2500000 = (N ) log2.5        divide both sides by log 2.5

16.077 = N ≈ 16 weeks