$\text{a)}a+\frac{4}{5}=1\frac{1}{4}$

$a=1\frac{1}{4}-\frac{4}{5}=1\frac{5}{20}-\frac{16}{20}=\frac{25}{20}-\frac{16}{20}=\frac{9}{20}$

$\text{Spr:}\frac{9}{20}+\frac{4}{5}=\frac{9}{20}+\frac{16}{20}=\frac{25}{20}=1\frac{5}{20}=1\frac{1}{4}$

$1\frac{4}{7}+b=3\frac{1}{3}$

$b=3\frac{1}{3}-1\frac{4}{7}=3\frac{7}{21}-1\frac{12}{21}=2\frac{28}{21}-1\frac{12}{21}=1\frac{16}{21}$

$\text{Spr:}1\frac{4}{7}+1\frac{16}{21}=1\frac{12}{21}+1\frac{16}{21}=2\frac{28}{21}=3\frac{7}{21}=3\frac{1}{3}$

$\text{b)}c-\frac{5}{6}=\frac{7}{9}$

$c=\frac{5}{6}+\frac{7}{9}=\frac{15}{18}+\frac{14}{18}=\frac{29}{18}=1\frac{11}{18}$

$\text{Spr:}1\frac{11}{18}-\frac{5}{6}=1\frac{11}{18}-\frac{15}{18}=\frac{29}{18}-\frac{15}{18}=\frac{14}{18}=\frac{7}{9}$

$d-1\frac{1}{4}=2\frac{2}{3}$

$d=1\frac{1}{4}+2\frac{2}{3}=1\frac{3}{12}+2\frac{8}{12}=3\frac{11}{12}$

$\text{Spr:}3\frac{11}{12}-1\frac{1}{4}=3\frac{11}{12}-1\frac{3}{12}=2\frac{8}{12}=2\frac{2}{3}$

$\text{c)}\frac{1}{2}-p=\frac{3}{7}$

$p=\frac{1}{2}-\frac{3}{7}=\frac{7}{14}-\frac{6}{14}=\frac{1}{14}$

$\text{Spr:}\frac{1}{2}-\frac{1}{14}=\frac{7}{14}-\frac{1}{14}=\frac{6}{14}=\frac{3}{7}$

$1\frac{1}{5}-u=\frac{5}{6}$

$u=1\frac{1}{5}-\frac{5}{6}=1\frac{6}{30}-\frac{25}{30}=\frac{36}{30}-\frac{25}{30}=\frac{11}{30}$

$\text{Spr:}1\frac{1}{5}-\frac{11}{30}=1\frac{6}{30}-\frac{11}{30}=\frac{36}{30}-\frac{11}{30}=\frac{25}{30}=\frac{5}{6}$