A=$\frac{3/4-3/5+3/7+3/11}{13/4-13/5+13/7+13/11}$
=$\frac{3(1/4-1/5+1/7+1/11}{13(1/4-1/5+1/7+1/11}$
=$\frac{3}{13}$
B=$\frac{( 3/10 - 4/15 - 7/20 ) * 5/19}{(1/14 + 1/7 + 3/35 ) * -4/3}$ =$\frac{(18/60-16/60-21/60)*5/19}{(5/70+10/70+16/70)*-4/3}$ =$\frac{-19/60*5/19}{3/10*-4/3}$ =$\frac{-1/12}{-2/5}$ =$\frac{5}{14}$