Đúng ghi Đ, sai ghi S?

a) 536 817 + 82 579 = 619 386

981 759 – 645 267 = 336 492

b) 64,38 + 93,46 = 157,84

86,09 – 54,3 = 31,79

c) \(\frac{4}{7} + \frac{3}{5} = \frac{{41}}{{35}}\)

\(\frac{{10}}{9} - \frac{5}{6} = \frac{5}{{18}}\)