1. rút gọn phân số
a. \(\dfrac{7}{35}\), \(\dfrac{18}{54}\),\(\dfrac{-15}{125}\),\(\dfrac{-4}{25}\)
b. \(\dfrac{27}{45}\),\(\dfrac{21}{28}\),\(\dfrac{8}{14}\), \(\dfrac{18}{-60}\), \(\dfrac{-270}{360}\)
c. \(\dfrac{3.4+3.7}{6.5+9}\)
d. \(\dfrac{-63}{81}\),\(\dfrac{9.6}{9.35}\), \(\dfrac{7.2+8}{2.14.5}\)