Check the picture below.
let's firstly convert the mixed fractions to improper fractions and then subtract.
[tex]\stackrel{mixed}{42\frac{1}{2}}\implies \cfrac{42\cdot 2+1}{2}\implies \stackrel{improper}{\cfrac{85}{2}} ~\hfill \stackrel{mixed}{67\frac{3}{7}}\implies \cfrac{67\cdot 7+3}{7}\implies \stackrel{improper}{\cfrac{472}{7}} \\\\[-0.35em] ~\dotfill\\\\ \cfrac{472}{7}~~ - ~~\cfrac{85}{2}\implies \cfrac{(2)472~~ - ~~(7)85}{\underset{\textit{using this LCD}}{14}}\implies \cfrac{944~~ - ~~595}{14}\implies \cfrac{349}{14}\implies 24\frac{13}{14}[/tex]
