c, 9.$3^{3}$.$\frac{1}{81}$.$3^{2}$
= ($3^{3}$.$3^{2}$).(9.$\frac{1}{81}$)
= $3^{3+2}$.$\frac{9}{81}$
= $3^{5}$.$\frac{1}{9}$
= 243.$\frac{1}{9}$
= $\frac{243}{9}$
= 27
d, $\frac{120^{3}}{40^{3}}$
= ($\frac{120}{40}$)$^{3}$
= $3^{3}$
= 27
Chúc bạn học tốt! ^^