a) $A= (-0.75-\frac{1}{4})/(-5)+\frac{1}{18}-(-\frac{1}{6})/(-3)$
$A= (-0.75-0.25)/(-5)+\frac{1}{18}-\frac{1}{18}=(-1)/(-5)=\frac{1}{5}$
b) $B= (\frac{6}{25}-1.24)/\frac{3}{7}/[(3\frac{1}{2}-3\frac{2}{3})/\frac{1}{14}]$
$B= (\frac{6}{25}-\frac{31}{25})/\frac{3}{7}/[(\frac{7}{2}-\frac{11}{3})/\frac{1}{14}]=(-1)/\frac{3}{7}/[(\frac{-1}{6})/\frac{1}{14}]=(\frac{-7}{3})/(\frac{-7}{3})=1$