L.C.M = $$2 \times 2 \times 2 \times 3= 24$$
$$\dfrac{3}{4} = \dfrac{3 \times 6 }{4 \times 6} = \dfrac{18}{24}$$
$$\dfrac{5}{6} = \dfrac{5 \times 4}{6 \times 4} = \dfrac{ 20}{24}$$
$$\dfrac{ 7}{8}= \dfrac{ 7 \times 3}{8 \times 3} = \dfrac{ 21}{24}$$
Thus, the given fractions are equivalent to
$$\dfrac{18}{24}, \dfrac{20 }{24} $$ and $$\dfrac{21}{24}$$ respectively.
(ii) $$\dfrac{7}{25}, \dfrac{9}{10}, \dfrac{19}{40}$$
First, we find L.C.M. of $$25, 10$$ and $$40$$
$$\therefore$$ L.C.M. is $$5 \times 5 \times 2 \times 2 \times 2= 200$$
$$\therefore \dfrac{7}{25} = \dfrac{7 \times 8}{25 \times 8}= \dfrac{56}{200}$$
$$\dfrac{9}{10} = \dfrac{9 \times 20}{10 \times 20}= \dfrac{180}{200}$$
$$\dfrac{19}{40} = \dfrac{19 \times 5}{95 \times 200}= \dfrac{95}{200}$$
Thus, the given fractions are equivalent to
$$\dfrac{56}{200}, \dfrac{180}{200}$$ and $$ \dfrac{95}{200}$$ respectively.