Step 1 :The inner function is \(u = x^{2} + 9\).
Step 2 :Deriving both sides of the equation \(u = x^{2} + 9\) with respect to \(x\) gives \(du = 2x dx\).
Step 3 :Isolating \(dx\) gives \(dx = \frac{du}{2x}\).
Step 4 :Substitute \(u = x^{2} + 9\) and \(dx = \frac{du}{2x}\) into the integral, we get \(\int_{0}^{4} \frac{6 x^{3}}{\sqrt{u}} \cdot \frac{du}{2x} = 3\int_{0}^{4} \frac{x^{2}}{\sqrt{u}} du\).
Step 5 :Substitute \(u = x^{2} + 9\) into the integral, we get \(3\int_{9}^{25} \frac{u - 9}{\sqrt{u}} du\).
Step 6 :Split the integral into two parts, we get \(3\int_{9}^{25} \frac{u}{\sqrt{u}} du - 3\int_{9}^{25} \frac{9}{\sqrt{u}} du\).
Step 7 :Simplify the integral, we get \(3\int_{9}^{25} u^{\frac{1}{2}} du - 27\int_{9}^{25} u^{-\frac{1}{2}} du\).
Step 8 :Integrate the integral, we get \(3[\frac{2}{3}u^{\frac{3}{2}}]_{9}^{25} - 27[2u^{\frac{1}{2}}]_{9}^{25}\).
Step 9 :Calculate the integral, we get \(2[25^{\frac{3}{2}} - 9^{\frac{3}{2}}] - 54[25^{\frac{1}{2}} - 9^{\frac{1}{2}}]\).
Step 10 :\boxed{2[25^{\frac{3}{2}} - 9^{\frac{3}{2}}] - 54[25^{\frac{1}{2}} - 9^{\frac{1}{2}}]} is the final answer.