a) $\dfrac23+5\dfrac37:2+\dfrac{9}{49}\cdot(-7)+\dfrac{1}{12}\cdot(-2)^4\\=\dfrac23+\dfrac{38}{7}:2+\dfrac{-9}{7}+\dfrac43\\=\dfrac63+\dfrac{19}{7}+\dfrac{-9}{7}\\=2+\dfrac{10}7\\=\dfrac{24}{7}$
c) $\left(2\dfrac13+3\dfrac12\right):\left(-4\dfrac15+3\dfrac17\right)+7\dfrac12\\=\left(\dfrac73+\dfrac72\right):\left(\dfrac{-25}6+\dfrac{22}7\right)+\dfrac{15}{2}\\=\dfrac{35}{6}:\dfrac{-43}{42}+\dfrac{15}{2}\\=\dfrac{-245}{43}+\dfrac{15}{2}\\=\dfrac{155}{86}$
