Ta tính lần lượt:

$A=\frac{\frac{−1}{2}−5 . (\frac{3}{2})^{2}}{15\frac{2}{9}+(−\frac{2}{3})^{2}}$

= $\frac{\frac{−1}{2}−5 . \frac{9}{4}}{\frac{137}{9}+\frac{4}{9}}$

= $\frac{\frac{−1}{2} − \frac{45}{4}}{\frac{47}{3}}$

=  $\frac{\frac{-47}{4}}{\frac{47}{3}}$

= $\frac{-3}{4}$

$B=\frac{7}{12} . 3,4 − \frac{7}{12} . 8,8$.

= $\frac{7}{12} . (3,4 − 8,8)$.

= $\frac{7}{12} . (-5,4)$

= $\frac{7}{12} .\frac{-27}{5}$

= $\frac{-63}{20}$

$A - 5B =  \frac{-3}{4} - 5 . \frac{-63}{20}$

= $\frac{-3}{4} + \frac{63}{4}$

= $15$