When you multiply 8•26 you get 208
Exponential equation is
y=a(b)ˣ
when b>1, it is growth
when 0>b>1, it is decay
so
we want the 2nd number to be more than 1
that would be the 3rd one, y=3(8)ˣ
To answer this question we can propose the following equation:

Where:
x is the number of weeks elapsed.
d is the debt depending on the weeks.
Robert promised to pay at least $ 67 each week.
Therefore, after 5 weeks the debt of rober should be:


Then scenario A) is possible because
.
After 6 weeks:


Then scenario B) is possible because
.
After 7 weeks


Then scenario C) is possible because
.
After 8 weeks


So scenario D) is NOT possible because 
Finally the correct answer is option D.