7\9-15\10= 18х4\15= 4\11х4 7\12= 1 3\4:21\24=

[latex]\\ \frac{7}{9} - \frac{15}{10} = \frac{7*10-15*9}{90} = \frac{70-135}{90} = -\frac{65}{90} =- \frac{13}{18} \\ \\ \frac{18*4}{15} = \frac{72}{15}=4,8\\ \\ \frac{4}{11}*4 \frac{7}{12} = \frac{4}{11} *\frac{55}{12} = \frac{220}{132} = \frac{110}{66}=1 \frac{44}{66}= 1\frac{22}{33} \\ \\ 1 \frac{3}{4}: \frac{21}{24} = \frac{7}{4} * \frac{24}{21} =2[/latex]