Giúp mik bài 1 nha Nếu dc làm bài 2 cũng dc ạ mik sẽ cho câu trả lời hay nhất

a,

$\dfrac{-5}{9}:\dfrac{-7}{18}+\dfrac{9}{7}$

$=\dfrac{-5}{9}.\dfrac{-18}{7}+\dfrac{9}{7}$

$=\dfrac{10}{7}+\dfrac{9}{7}$

$=\dfrac{19}{7}$

b,

$\dfrac{2^{27}.9^4}{6^9.85}$

$=\dfrac{2^{27}.3^8}{2^9.3^9.5.17}$

$=\dfrac{2^{18}}{3.5.17}$

$=\dfrac{2^{18}}{255}$