Ответ:

  1. \(-7+(-8)=-(7+8)=-15\).
  2. \(-0,38+(-0,74)=-(0,38+0,74)=-1,12\).
  3. \(-1,8+(-0,34)=-(1,8+0,34)=-2,14\).
  4. \(-4\frac{6}{7}+(-2\frac{3}{7})=-(4\frac{6}{7}+2\frac{3}{7})=-7\frac{2}{7}\).
  5. \(-\frac{5}{6}+(-\frac{7}{8})=-\left(\frac{20}{24}+\frac{21}{24}\right)=-\frac{41}{24}=-1\frac{17}{24}\).
  6. \(-6\frac{7}{15}+(-8\frac{3}{10})=-\left(6\frac{14}{30}+8\frac{9}{30}\right)=-14\frac{23}{30}\).

Ответ: 1) −15; 2) −1,12; 3) −2,14; 4) −7 2/7; 5) −1 17/24; 6) −14 23/30.