\(a,=\dfrac{12341234}{123512345}=\dfrac{4}{55}\\ b,=\dfrac{3}{2}.\left(\dfrac{5}{4}.\dfrac{8}{5}\right):\dfrac{2021}{2022}\\ =\dfrac{3}{2}.\dfrac{2}{1}:\dfrac{2021}{2022}\\ =3.\dfrac{2022}{2021}=\dfrac{6066}{2021}\\ c,=\dfrac{3.3+4.4-5}{12}=\dfrac{20}{12}=\dfrac{5}{3}\)