a)
y=6\sqrt[3]x-4\sqrt[4]x=6*x^{\frac{1}{3}}-4*x^{\frac{1}{4}}
y^'=6*\frac{1}{3}*x^{\frac{1}{3}-1}-4*\frac{1}{4}*x^{\frac{1}{4}-1}=2x^{-\frac{2}{3}}-x^{-\frac{3}{4}}=2\frac{1}{\sqrt[3]x^2}-\frac{1}{\sqrt[4]x^3}=\frac{2}{\sqrt[3]{x^2}}-\frac{1}{\sqrt[4]{x^3}}