let's firstly convert the mixed fractions to improper fractions.
[tex]\bf \stackrel{mixed}{3\frac{3}{4}}\implies \cfrac{3\cdot 4+3}{4}\implies \stackrel{improper}{\cfrac{15}{4}} ~\hfill \stackrel{mixed}{5\frac{1}{4}}\implies \cfrac{5\cdot 4+1}{4}\implies \stackrel{improper}{\cfrac{21}{4}} \\\\[-0.35em] \rule{34em}{0.25pt}\\\\ \cfrac{15}{4}\div\cfrac{21}{4}\implies \cfrac{15}{4}\div\cfrac{4}{21}\implies \cfrac{15}{21}\cdot \cfrac{4}{4}\implies \cfrac{5}{7}\cdot 1\implies \cfrac{5}{7}[/tex]
