3 4/5 +1 4/5 ;1 4/5 +7 7/18 ; 8 4/5 + 2 1/3 ; 12 5/6 +4/15 ; 7/20 +2 7/10; 8 3/7 +1 9/14

$3 \frac{4}{5} +1 \frac{4}{5}=5 \frac{3}{5}$

$1\frac{4}{5} +7\frac{7}{18} =\frac{9}{5} +\frac{133}{18} =\frac{9*18+133*5}{90} =\frac{827}{90}=9\frac{17}{90}$

$8\frac{4}{5} + 2\frac{1}{3}=\frac{44}{5} +\frac{7}{3}=\frac{44*3+7*5}{15}=\frac{167}{15}=11\frac{2}{15}$

$12\frac{5}{6}+\frac{4}{15}=\frac{77}{6}+\frac{4}{15}=\frac{77*5+4*2}{30}=\frac{393}{30}=13\frac{3}{30}=13\frac{1}{10}$

$\frac{7}{20}+2\frac{7}{10}=\frac{7}{20}+\frac{27}{10}=\frac{7+27*2}{20}=\frac{61}{20}=3\frac{1}{20}$

$8\frac{3}{7} +1\frac{9}{14}=\frac{59}{7}+\frac{23}{14}=\frac{59*2+23}{14}=\frac{141}{14}=10\frac{1}{14}$