i) We classified the rational number with same denominators.

= (2+(-4))/5 + (7+(-1))/3
= (2-4)/5 + (7-1)/3
= -2/5 + 6/3

L.C.M for 5 and 3 is 15

\(= \frac{(-2\times3)}{(5\times3)}+\frac{(6\times5)}{(3\times5)}\\=\frac{-6}{15}+\frac{30}{15}\)

Now the given denominators are same, we add it.

\(\frac{(-6+30)}{15}\\=\frac{24}{15}\\=\frac{8}{5}\)

ii) We classified the rational number with same denominators.

 = 3/7 + (-11/7) + (-4/9) + 7/9

\(=\frac{(3+(-11))}{7}+\frac{(-4+7)}{9}\\=\frac{-8}{7}+\frac{3}{9}\\=\frac{-8}{7}+\frac{1}{3}\)

L.C.M for 7 and 3 is 21

\(=\frac{(-8\times3)}{(7\times3)}+\frac{(1\times7)}{(3\times7)}\\=\frac{-24}{21}+\frac{7}{21}\\=\frac{(-24+7)}{21}\\=\frac{-17}{21}\)

iii) We classified the rational number with same denominators.

2/5 + 4/5 + 8/3 + (-2/3) + (-11/15)

Now the given denominators are same, we add it.

\(=\frac{(2+4)}{5}+\frac{(8+(-2))}{3}+\frac{-11}{15}\\=\frac{6}{5}+\frac{(8-2)}{3}+\frac{-11}{15}\\=\frac{6}{5}+\frac{2}{1}+\frac{-11}{15}\)

L.C.M for 5,1 and 15 is 15

\(=\frac{(6\times3)}{(5\times3)}+\frac{(2\times15)}{(1\times15)}+\frac{(-11\times1)}{(15\times1)}\\=\frac{-18}{15}+\frac{30}{15}+\frac{-11}{15}\\=\frac{(18+30+(-11))}{15}\\=\frac{(18+30-11)}{15}\\=\frac{37}{15}\)