Can someone help on this? Please :)

N(t)=2×

17

15

step by step explain:

before lesson (t=0), she knows 2 words.

after a week (t=1), she knows

2×(1+70%)=3.4 words

after one more week (t=2), she knows

3.4×(1+70%)=5.78 words

one more week later (t=3), she knows

5.78×(1+70%)=9.826 words

and so on ...

from pattern shown above, we know that she knows

2× words after t weeks

so N(t)=2×

after 4 weeks (t=4), she knows 2×=16.7042≈17 words

for learning 5000 words, she need:

2×=5000

   =2500

t log(1.7)=log(2500)

         t=

          =14.7448727

          ≈15 (round up)

b

step-by-step explanation: