let's first off, convert all mixed fractions to improper fractions, and then add.
[tex]\bf \stackrel{mixed}{17\frac{1}{3}}\implies \cfrac{17\cdot 3+1}{3}\implies \stackrel{improper}{\cfrac{52}{3}} \\\\\\ \stackrel{mixed}{6\frac{1}{4}}\implies \cfrac{6\cdot 4+1}{4}\implies \stackrel{improper}{\cfrac{25}{4}}~\hfill \stackrel{mixed}{4\frac{2}{3}}\implies \cfrac{4\cdot 3+2}{3}\implies \stackrel{improper}{\cfrac{14}{3}} \\\\[-0.35em] \rule{34em}{0.25pt}[/tex]
[tex]\bf \stackrel{week~1}{6\frac{1}{4}}+\stackrel{week~2}{4\frac{2}{3}}+\stackrel{week~3}{x}=17\frac{1}{3}~\hfill \implies ~\hfill \cfrac{25}{4}+\cfrac{14}{3}+x=\cfrac{52}{3} \\\\[-0.35em] ~\dotfill\\\\ \stackrel{\textit{multiplying both sides by }\stackrel{LCD}{12}}{12\left( \cfrac{25}{4}+\cfrac{14}{3}+x \right)=12\left( \cfrac{52}{3} \right)}\implies (3)25+(4)14+(12)x=(4)52 \\\\\\ 75+56+12x=208\implies 131+12x=208\implies 12x=77 \\\\\\ x=\cfrac{77}{12}\implies x=6\frac{5}{12}[/tex]