I believe the sides of the suare is 9
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.
let's firstly convert the mixed fractions to improper fractions.
![\bf \stackrel{mixed}{3\frac{1}{2}}\implies \cfrac{3\cdot 2+1}{2}\implies \stackrel{improper}{\cfrac{7}{2}}~\hfill \stackrel{mixed}{1\frac{1}{3}}\implies \cfrac{1\cdot 3+1}{3}\implies \stackrel{improper}{\cfrac{4}{3}} \\\\[-0.35em] \rule{34em}{0.25pt}](https://tex.z-dn.net/?f=%5Cbf%20%5Cstackrel%7Bmixed%7D%7B3%5Cfrac%7B1%7D%7B2%7D%7D%5Cimplies%20%5Ccfrac%7B3%5Ccdot%202%2B1%7D%7B2%7D%5Cimplies%20%5Cstackrel%7Bimproper%7D%7B%5Ccfrac%7B7%7D%7B2%7D%7D~%5Chfill%20%5Cstackrel%7Bmixed%7D%7B1%5Cfrac%7B1%7D%7B3%7D%7D%5Cimplies%20%5Ccfrac%7B1%5Ccdot%203%2B1%7D%7B3%7D%5Cimplies%20%5Cstackrel%7Bimproper%7D%7B%5Ccfrac%7B4%7D%7B3%7D%7D%20%5C%5C%5C%5C%5B-0.35em%5D%20%5Crule%7B34em%7D%7B0.25pt%7D)
![\bf \begin{array}{ccll} miles&hours\\ \cline{1-2}\\ \frac{7}{2}&1\\[0.8em] m&\frac{4}{3} \end{array}\implies \cfrac{~~\frac{7}{2}~~}{m}=\cfrac{~~1~~}{\frac{4}{3}}\implies \cfrac{7}{2m}=\cfrac{3}{4}\implies 28=6m \\\\\\ \cfrac{28}{6}=m\implies \cfrac{14}{3}=m\implies 4\frac{2}{3}=m](https://tex.z-dn.net/?f=%5Cbf%20%5Cbegin%7Barray%7D%7Bccll%7D%20miles%26hours%5C%5C%20%5Ccline%7B1-2%7D%5C%5C%20%5Cfrac%7B7%7D%7B2%7D%261%5C%5C%5B0.8em%5D%20m%26%5Cfrac%7B4%7D%7B3%7D%20%5Cend%7Barray%7D%5Cimplies%20%5Ccfrac%7B~~%5Cfrac%7B7%7D%7B2%7D~~%7D%7Bm%7D%3D%5Ccfrac%7B~~1~~%7D%7B%5Cfrac%7B4%7D%7B3%7D%7D%5Cimplies%20%5Ccfrac%7B7%7D%7B2m%7D%3D%5Ccfrac%7B3%7D%7B4%7D%5Cimplies%2028%3D6m%20%5C%5C%5C%5C%5C%5C%20%5Ccfrac%7B28%7D%7B6%7D%3Dm%5Cimplies%20%5Ccfrac%7B14%7D%7B3%7D%3Dm%5Cimplies%204%5Cfrac%7B2%7D%7B3%7D%3Dm)