a,$\frac{7}{5}$ + $\frac{4}{7}$ - $\frac{9}{10}$
= $\frac{98}{70}$+$\frac{40}{70}$-$\frac{63}{70}$
= $\frac{98+40-63}{70}$
=$\frac{75}{70}$
=$\frac{15}{14}$
b, 2 + $\frac{3}{4}$ x $\frac{8}{5}$
= 2+ $\frac{3x8}{4x5}$
= 2 + $\frac{24}{20}$
= 2 + $\frac{6}{5}$
= $\frac{10}{5}$ + $\frac{6}{5}$
= $\frac{10+6}{5}$
=$\frac{16}{5}$
c, $\frac{9}{8}$-$\frac{6}{5}$:$\frac{8}{5}$
=$\frac{9}{8}$-$\frac{6}{5}$x$\frac{5}{8}$
=$\frac{9}{8}$-$\frac{6x5}{5x8}$
=$\frac{9}{8}$-$\frac{3}{4}$
=$\frac{9}{8}$-$\frac{6}{8}$
=$\frac{9-6}{8}$
=$\frac{3}{8}$
d,6:$\frac{9}{7}$x$\frac{3}{10}$
=6x$\frac{7}{9}$x$\frac{3}{10}$
= $\frac{6x7x3}{9x10}$
=$\frac{126}{90}$
=$\frac{7}{5}$