(3/4-4/5)*7,8+(2/3+4/7)*7/13

1) $\frac{3}{4} - \frac{4}{5} = \frac{15}{20} - \frac{16}{20} =- \frac{1}{20}$
2) $-\frac{1}{20} * 7\frac{8}{10} = -\frac{1}{20} * \frac{78}{10} = -\frac{78}{200} =-0.39$
3) $\frac{2}{3} + \frac{4}{7} = \frac{14}{21} + \frac{12}{21} = \frac{26}{21} = 1\frac{5}{21}$
4) $\frac{26}{21} * \frac{7}{13} = \frac{182}{273}$
5) $\frac{78}{200} + \frac{182}{273} = \frac{21294}{54600} + \frac{36400}{54600} = \frac{57694}{54600} = 1\frac{3094}{54600} =1 \frac{1547}{27300} = 1\frac{221}{3900}$