2 3 8 ? 1 5 9

$7\frac{6}{3}-7\frac{6}{7}=\frac{27}{3}-\frac{55}{7}=\frac{189}{21}-\frac{165}{21}=\frac{189-165}{21}=\frac{24}{21}=\frac{8}{7}$

$9\frac{3}{4}-5\frac{3}{5}=\frac{39}{4}-\frac{28}{5}=\frac{195}{20}-\frac{112}{20}=\frac{195-112}{20}=\frac{{\displaystyle 83}}{{\displaystyle 20}}$

$3\frac{3}{8}\times 4\frac{2}{5}=\frac{27}{8}\times \frac{22}{5}=\frac{27\times 22}{8\times 5}=\frac{594}{40}=\frac{297}{20}$

$3\frac{2}{7}÷1\frac{3}{8}=\frac{23}{7}÷\frac{11}{8}=\frac{23}{7}\times \frac{8}{11}=\frac{184}{77}$