\(A=\frac{7}{19}\cdot\frac{8}{11}+\frac{7}{19}\cdot\frac{3}{11}+\frac{12}{19}\)
\(A=\frac{7}{19}\cdot\left(\frac{8}{11}+\frac{3}{11}\right)+\frac{12}{19}\)
\(A=\frac{7}{9}\cdot1+\frac{12}{19}\)
\(A=\frac{7}{19}+\frac{12}{19}=\frac{19}{19}=1\)
\(B=\frac{5}{9}\cdot\frac{7}{13}+\frac{5}{9}+\frac{9}{13}-\frac{5}{9}\cdot\frac{3}{13}\)
\(B=\frac{5}{9}\cdot\left(\frac{7}{13}+\frac{9}{13}-\frac{3}{13}\right)\)
\(B=\frac{5}{9}\cdot1=\frac{5}{9}\)
\(C=\left(\frac{67}{111}+\frac{2}{33}-\frac{15}{117}\right)\cdot\left(\frac{1}{3}-\frac{1}{4}-\frac{1}{12}\right)\)
\(C=\left(\frac{67}{111}+\frac{2}{33}-\frac{15}{117}\right)\cdot\left(\frac{4}{12}-\frac{3}{12}-\frac{1}{12}\right)\)
\(C=\left(\frac{67}{111}+\frac{2}{33}-\frac{15}{117}\right)\cdot0=0\)
