let's firstly convert the mixed fractions to improper fractions and then add up all four days.
[tex]\bf \stackrel{mixed}{16\frac{3}{4}}\implies \cfrac{16\cdot 4+3}{4}\implies \stackrel{improper}{\cfrac{67}{4}}~\hfill \stackrel{mixed}{12\frac{3}{4}}\implies \cfrac{12\cdot 4+3}{4}\implies \cfrac{47}{4} \\\\[-0.35em] ~\dotfill\\\\ \stackrel{\textit{all 4 days summed up}}{\cfrac{67}{4}+\cfrac{47}{4}}\implies \cfrac{67+47}{4}\implies \cfrac{114}{4}\implies \cfrac{57}{2}\implies 28\frac{1}{2}[/tex]
