First thing you have to find LCD ( lowest common denominator) 12 is the lowest one:
[tex]126\frac{1}{4}=126\frac{3}{12}[/tex]
[tex]78\frac{2}{3}=78\frac{8}{12}[/tex]
now its all about substraction:
[tex]126\frac{3}{12}-78\frac{8}{12}=47\frac{7}{12}[/tex]
so the difference is [tex]47\frac{7}{12}[/tex]
or you can do it in a bit diffrent way
[tex]126\frac{1}{4}=126\frac{3}{12}=\frac{126*12+3}{12}=\frac{1515}{12}[/tex]
[tex]78\frac{2}{3}=78\frac{8}{12}=\frac{78*12+8}{12}=\frac{944}{12}[/tex]
substraction again:
[tex]\frac{1515}{12}-\frac{944}{12}=\frac{571}{12}=47\frac{7}{12}[/tex]
