a)

• ${\left(-2\frac{1}{3}a\right)}^2={\left(-2\frac{1}{3}\right)}^2\cdot a^2={\left(-\frac{7}{3}\right)}^2\cdot a^2=\frac{49}{9}\cdot a^2=5\frac{4}{9}\cdot a^2$

• ${\left(-3\frac{1}{2}bx\right)}^3={\left(-3\frac{1}{2}\right)}^3\cdot b^3\cdot x^3={\left(-\frac{7}{2}\right)}^3\cdot b^3\cdot x^3=\frac{49}{4}\cdot \left(-\frac{7}{2}\right)\cdot b^3\cdot x^3=$

$=-\frac{343}{8}\cdot b^3\cdot x^3=-42\frac{7}{8}\cdot b^3\cdot x^3$