Giúp mình với mọi người ơi

a) $\dfrac{6}{18}$ + $\dfrac{7}{9}$ = $\dfrac{3}{9}$ + $\dfrac{7}{9}$ = $\dfrac{10}{9}$

b) $\dfrac{7}{36}$ + $\dfrac{5}{9}$ = $\dfrac{7}{36}$ + $\dfrac{30}{36}$ = $\dfrac{37}{36}$

c) $\dfrac{45}{56}$ - $\dfrac{12}{8}$ = $\dfrac{45}{56}$ - $\dfrac{84}{56}$ = $\dfrac{-39}{56}$

d) 4 + $\dfrac{7}{9}$ = $\dfrac{4}{1}$ + $\dfrac{7}{9}$ = $\dfrac{36}{9}$ + $\dfrac{7}{9}$ = $\dfrac{43}{9}$

e) 6 - $\dfrac{12}{5}$ = $\dfrac{6}{1}$ - $\dfrac{12}{5}$ = $\dfrac{30}{5}$ - $\dfrac{12}{5}$ =  $\dfrac{18}{5}$

f) $\dfrac{5}{8}$ + $\dfrac{5}{12}$ = $\dfrac{60}{96}$ + $\dfrac{40}{96}$ = $\dfrac{100}{96}$ = $\dfrac{25}{24}$

i) $\dfrac{2}{5}$ x $\dfrac{6}{7}$ = $\dfrac{12}{35}$

j) $\dfrac{7}{4}$ x $\dfrac{6}{5}$ = $\dfrac{42}{20}$ = $\dfrac{21}{10}$

g) $\dfrac{1}{6}$ x $\dfrac{6}{4}$ = $\dfrac{1}{4}$

h) $\dfrac{3}{8}$ x $\dfrac{4}{9}$ = $\dfrac{12}{72}$ = $\dfrac{1}{6}$

i) $\dfrac{5}{9}$ x $\dfrac{12}{15}$ = $\dfrac{60}{135}$ = $\dfrac{12}{27}$ = $\dfrac{4}{9}$

j) $\dfrac{6}{5}$ x $\dfrac{10}{3}$ = $\dfrac{60}{15}$ = 4

k) 4 x $\dfrac{6}{4}$ = $\dfrac{4}{1}$ x $\dfrac{6}{4}$ = $\dfrac{6}{1}$ = 6

l) $\dfrac{4}{9}$ x 7 = $\dfrac{4}{9}$ x $\dfrac{7}{1}$ = $\dfrac{28}{9}$

m) 6 x $\dfrac{15}{5}$ = 6 x 3 = 18

v) $\dfrac{7}{8}$ x 2 = $\dfrac{7}{8}$ x $\dfrac{2}{1}$ = $\dfrac{7}{4}$