TeX source:

y^{\prime}=\frac{1}{3}\left(3 x^{2}+15\right)^{-2 / 3} \cdot D\left(3 x^{2}+15\right)=\frac{1}{3}\left(3 x^{2}+15\right)^{-2 / 3} \cdot(6 x)