12/13-15/26 9/28-11/35 39/40-19/28

[latex] \frac{12}{13} - \frac{15}{26} = \frac{24}{26} - \frac{15}{26} = \frac{9}{26} [/latex] [latex] \frac{9}{28} -\frac{11}{35} =\frac{45}{140} - \frac{44}{140}= \frac{1}{140} [/latex] [latex] \frac{39}{40} - \frac{19}{28} = \frac{273}{280} - \frac{190}{280}= \frac{83}{280} [/latex]