Thực hiện phép tính (hợp lí nếu có thể):
a) (\(\dfrac{-6}{11}\)) . \(\dfrac{7}{10}\) . \(\dfrac{11}{-6}\) . (-20)
b) (\(-1\dfrac{1}{2}\)) : \(\dfrac{3}{4}\) . \(-4\dfrac{1}{2}\))
c) \(13\dfrac{2}{7}\) : (\(\dfrac{-8}{9}\)) + \(2\dfrac{5}{7}\) : (\(\dfrac{-8}{9}\))