Tomamos como el límite
$$\lim_{x \to \frac{5^{\frac{2}{3}}}{5}^+}\left(\frac{6 x^{4} + 3 x^{3}}{5 x^{3} + 1}\right)$$
cambiamos
$$\lim_{x \to \frac{5^{\frac{2}{3}}}{5}^+}\left(\frac{6 x^{4} + 3 x^{3}}{5 x^{3} + 1}\right)$$
=
$$\lim_{x \to \frac{5^{\frac{2}{3}}}{5}^+}\left(\frac{3 x^{3} \left(2 x + 1\right)}{5 x^{3} + 1}\right)$$
=
$$\lim_{x \to \frac{5^{\frac{2}{3}}}{5}^+}\left(\frac{x^{3} \left(6 x + 3\right)}{5 x^{3} + 1}\right) = $$
$$\frac{\left(\frac{5^{\frac{2}{3}}}{5}\right)^{3} \left(3 + 6 \frac{5^{\frac{2}{3}}}{5}\right)}{1 + 5 \left(\frac{5^{\frac{2}{3}}}{5}\right)^{3}} = $$
= 3/10 + 3*5^(2/3)/25
Entonces la respuesta definitiva es:
$$\lim_{x \to \frac{5^{\frac{2}{3}}}{5}^+}\left(\frac{6 x^{4} + 3 x^{3}}{5 x^{3} + 1}\right) = \frac{3}{10} + \frac{3 \cdot 5^{\frac{2}{3}}}{25}$$