Hi johana,
schreibe als Potenzen um ;).
a)
$$\sqrt{\sqrt[3]{s^6t^{12}}} = ((s^6t^{12})^{\frac13})^{\frac12} = (s^6t^{12})^{\frac16} = st^2$$
b)
$$4^{\frac{3n}{n}}3^{\frac{m^2}{m}} = 4^33^m = 64\cdot3^m$$
c)
$$(x^6(x^5x^{\frac44})^{\frac13})^{\frac14} = (x^6(x^6)^{\frac13})^{\frac14} = (x^6x^2)^{\frac14} = (x^8)^{\frac{1}{4}} = x^2$$
Grüße
